tag:blogger.com,1999:blog-40708552024-03-13T06:30:37.747-07:00Gauge InvarianceUnknownnoreply@blogger.comBlogger94125tag:blogger.com,1999:blog-4070855.post-11124410135276658212022-03-08T21:16:00.006-08:002022-03-08T21:35:16.135-08:00List of talks given by members of my group at APS March Meeting:<div class="separator" style="clear: both;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEj08lAQXGMQbdaTJ5Gb_LVgxA8_BgDiGKeSQEuT-QnAZIQF9lNh9vdcabfWGrducRNPY9ZPYM8_vAT04fe0ZwE2rk1f4fq_rLWDi4gYoXuAnnKO7iJF_OkJakqkeUCAgbMUsOybPpUg0_XGuhnGRpSB57FppaOc1P2d3tavUSmdvmn4kQTo6A=s2880" style="display: block; padding: 1em 0; text-align: center; "><img alt="" border="0" width="400" data-original-height="1800" data-original-width="2880" src="https://blogger.googleusercontent.com/img/a/AVvXsEj08lAQXGMQbdaTJ5Gb_LVgxA8_BgDiGKeSQEuT-QnAZIQF9lNh9vdcabfWGrducRNPY9ZPYM8_vAT04fe0ZwE2rk1f4fq_rLWDi4gYoXuAnnKO7iJF_OkJakqkeUCAgbMUsOybPpUg0_XGuhnGRpSB57FppaOc1P2d3tavUSmdvmn4kQTo6A=s400"/></a></div>
Xuexin Xu: B36.00014 Mon 2:06 PM<br>
Arne Schlabes: K41.00012 Tue 5:12 PM<br>
Myself: W41.00008 Thurs 4:48 PM<br>
Manabputra: W41.00009 Thurs 5:00 PM<br>
Alwin van Steensel: Y35.00013 Fri. 10:48 AM<br>
Josephine Pazem: Z36.00012 Fri 1:42 PM<br><br>
and posters too.<br><br>
#apsmarch #fzjuelich #rwthaachenUnknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-46596598916460557802022-03-08T20:49:00.002-08:002022-03-08T20:49:28.148-08:00Parasitic-free gate: A protected switch between idle and entangled states <div class="separator" style="clear: both;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgiTyCIGMSEAy-Voi8B-L5Ko7FHaEHJ7d-lRafnoJc7di3CKtp_yYXC85_2SmiMewH7IIlAD7ALht2nsCcDXXLZvl7jqjGlRzJPUAyypqUip2t65vYoP_lOSTQ7sx59ulbNy2HM82dAEtsIZGu2by1PR_Ip40dUCKA540lWQNGioLYA6_KNgg=s1210" style="display: block; padding: 1em 0; text-align: center; "><img alt="" border="0" width="320" data-original-height="1146" data-original-width="1210" src="https://blogger.googleusercontent.com/img/a/AVvXsEgiTyCIGMSEAy-Voi8B-L5Ko7FHaEHJ7d-lRafnoJc7di3CKtp_yYXC85_2SmiMewH7IIlAD7ALht2nsCcDXXLZvl7jqjGlRzJPUAyypqUip2t65vYoP_lOSTQ7sx59ulbNy2HM82dAEtsIZGu2by1PR_Ip40dUCKA540lWQNGioLYA6_KNgg=s320"/></a></div>
We propose a protected 2-qubit gate composed of two sub-gates that switches between idling and entangling modes. These sub-gates are separated by a large energy barrier. In superconducting circuits, this gate is derived by harnessing microwave driving and coupling modulation. The idle mode decouples qubits and leaves them with highly localized wave functions. The entangled mode, however, makes them interact in absence of the adversarial ZZ interactions. Our theoretical results show that this gate is a promising way to switch on and off a fast and high fidelity 2-qubit interaction.
Read further details <a href="https://arxiv.org/abs/2202.05208" target="_blank">here</a>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-30195802460613928362019-05-08T05:28:00.004-07:002019-05-08T05:31:14.451-07:00PhD position in my group<div dir="ltr" style="text-align: left;" trbidi="on">
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The theory groups at the Institute for Quantum Information of the Jülich-Aachen Research Alliance (JARA) are looking for a highly motivated candidate to fill a PhD position over the next few months. The doctoral project will focus on theoretical studies of physical implementations of quantum information processing, such as superconducting qubits, and enabling quantum technologies. The projects will be supervised by Dr. M.H. Ansari and may involve collaborations with leading experimental groups.<br />
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Master’s degree (or equivalent) in theoretical condensed matter physics or a related field and proficiency in English are required. Preference will be given to candidates with experience in quantum transport and open quantum systems, but strong candidates from other fields are encouraged to apply.<br />
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The application material should include:<br />
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<li>Short letter of motivation (less than a page)</li>
<li>CV and transcripts</li>
<li>Contact details (names and emails) of two possible referees</li>
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For further information about the group see the group webpage: <a href="https://sites.google.com/site/mansari">https://sites.google.com/site/mansari</a>. <br />
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To submit an application please email your documents to <a href="mailto:m.ansari@fz-juelich.de">m.ansari@fz-juelich.de</a>. Review of applications will start immediately and continue until all the position is filled.</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-13741494447000520052019-02-19T02:08:00.000-08:002019-02-19T02:08:11.499-08:00New Physics talk<div dir="ltr" style="text-align: left;" trbidi="on">
Recently I was invited to give a Quantum Information Seminar at Physics department of Syarcuse University, NY. There was a broad audience from high energy physics to cosmology, quantum chemistry, gravity and black holes and quantum computation, both experimentalists and theorists. My talk was about a new correspondence we found recently between physics and information. Below you can find my abstract, for questions contact me. <div>
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<a href="http://physics.syr.edu/event-items/2019/2019-01-17%20Mohammad%20Ansari.html" target="_blank">Link to Quantum Information Seminars at Syracuse</a></div>
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New Physics from Quantum Information Theory by Dr. Mohammad Ansari</h1>
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<strong style="box-sizing: border-box;">Jan 17, 2019 at 11:00 AM - 12:00 PM</strong></div>
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Room: 202 Physics Bldg.</div>
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In quantum physics physical quantities are linear in density matrix, e.g. energy, current, spin, etc. However, this is not the case in quantum information theory as informational measures are nonlinear functions in density matrix; examples are entropy, fidelity loss, purity, etc. Is there any way to measure information in the lab using physical quantities? This is an important question that I’ll address in this talk. I’ll present a new correspondence between entropy and physical quantities. I will discuss how this correspondence may introduce new physics in quantum heat engines, quantum computation, black holes, etc..</div>
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<strong style="box-sizing: border-box;">Dr. Mohammad Ansari, </strong>Julich Research Center, Germany</div>
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Host: Britton Plourde. Contact: Yudaisy Salomon Sargenton - phyadmin@syr.edu</div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-29737694689189664372018-10-08T02:48:00.002-07:002018-11-24T06:08:40.818-08:00Donna Strickland<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://3.bp.blogspot.com/-W3__Qw5yVeE/W7so7T1Ld5I/AAAAAAABJoI/tuuHh3A_d5c2XwCA9OzQF0HAoRwbWlwtACLcBGAs/s1600/IMG_2429.JPG" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1122" height="320" src="https://3.bp.blogspot.com/-W3__Qw5yVeE/W7so7T1Ld5I/AAAAAAABJoI/tuuHh3A_d5c2XwCA9OzQF0HAoRwbWlwtACLcBGAs/s320/IMG_2429.JPG" width="224" /></a>
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The lady who taught us nonlinear optics in Waterloo during my PhD studies just received a Nobel Prize in Physics! Dr Donna Strickland is nice, honest, and down-to-earth modest, such that I could not shamefully believe that she is better than others! She was excellent teacher also and was delivering science very well to students, and always with a taste of sweetness!<br />
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Her story of being so humble remind me of the following poem by Emily Dickinson:<br />
I'm Nobody! Who are you?<br />
Are you -Nobody- too?<br />
Then there's a pair of us!<br />
Don't tell! they'd...</div>
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...<br />
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<iframe allowfullscreen="" frameborder="0" height="275" src="https://www.linkedin.com/embed/feed/update/urn:li:share:6452841016658530304" width="504"></iframe></div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-64346389880584002252018-09-27T01:24:00.001-07:002018-09-27T05:20:48.963-07:00Postdoctoral Researcher in Quantum Information and Thermodynamics<div dir="ltr" style="text-align: left;" trbidi="on">
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<a href="https://1.bp.blogspot.com/-CPk5xtqhBTU/W6yTnJ84kxI/AAAAAAABIXY/jde8SA9x_EUioSC9V7WTKCrtBNbXw-gOQCPcBGAYYCw/s1600/IT_Ju%25CC%2588lich-3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="307" data-original-width="460" height="213" src="https://1.bp.blogspot.com/-CPk5xtqhBTU/W6yTnJ84kxI/AAAAAAABIXY/jde8SA9x_EUioSC9V7WTKCrtBNbXw-gOQCPcBGAYYCw/s320/IT_Ju%25CC%2588lich-3.jpg" width="320" /></a></div>
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The institute of Theoretical Nanoelectronics (PGI-2) concerns itself with investigating structure formation in condensed matter, starting on electronic length and time scales while bearing in mind macroscopic consequences. These studies are closely connected in diverse ways with experimental work within the institute, and also with projects in other institutes at Forschungszentrum Jülich.<br />
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The main focus of our work is placed on the electronic structure of solids, in particular with regard to their importance in information technology and cooperative phenomena in condensed matter. Research questions here concern dynamic structure formation processes together with the statistical mechanics of order and disorder processes. Special topics in the field of complex fluids deal with the structure and dynamics of soft matter.</div>
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<strong style="margin: 0px; padding: 0px;">We are looking to recruit as soon as possible a</strong></div>
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Postdoctoral Researcher in Quantum Information and Thermodynamics</h1>
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<strong style="margin: 0px; padding: 0px;">Your Job:</strong></div>
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<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">studying quantum heat engines in presence of enviornmental disturbance</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">understanding information-to-work process in superconductiong quantum computational devices</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">studying the analogue of fluctuation-dissipation theorem in quantum theory</li>
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<strong style="margin: 0px; padding: 0px;">Your Profile:</strong></div>
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<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">PhD degree (or nearly graduating) in theoretical condensed matter physics or a related field</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Preference will be given to cadidates with background experience in Quantum computation, condensed matter, statistical mechanics, and related Topics. Strong candidates from other fields are encouraged to apply</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Ability and willingness to work in an international, interdisciplinary and distributed teams as well as to assume responsibility</li>
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<div style="font-size: 15px; line-height: 1.5; margin-bottom: 0.77em; padding: 0px;">
<strong style="margin: 0px; padding: 0px;">Our Offer:</strong></div>
<ul style="box-sizing: border-box; list-style-image: none; list-style-position: initial; margin: 0px 0px 20px; padding: 0px 0px 0px 20px;">
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">a varied and challenging area of responsibility in an interdisciplinary team</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Exciting work setting on an attractive research campus with a very good infrastructure, ideally situated within the city triangle of Cologne, Düsseldorf, and Aachen</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">A comprehensive further training programme, including German language courses</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Flexible working hours and various opportunities to reconcile work and family life</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Limited for 1 years with possible longer-term prospects</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Full-time position with the option of <a class="external" href="https://www.hrecruiting.de/data/t5ChjatkIfdwmACO/Info_Vollzeitnah_en.pdf" style="background-image: url("http://www.fz-juelich.de/SiteGlobals/Frontend/Images/icons/sprite.png?__blob=normal"); background-position: 1px -147px; background-repeat: no-repeat no-repeat; box-sizing: border-box; color: #004176; margin: 0px; padding: 0px 0px 0px 13px; text-decoration: none;" target="_blank" title="External link slightly reduced (Opens new window)">slightly reduced</a> working hours</li>
<li style="box-sizing: border-box; font-size: 15px; line-height: 1.5; margin: 0.3em 0px 0px; padding: 0px;">Salary and social benefits in conformity with the provisions of the Collective Agreement for the Civil Service (TVöD)</li>
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Forschungszentrum Jülich aims to employ more women in this area and therefore particularly welcomes applications from women.<br />
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We also welcome applications from disabled persons.</div>
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<a href="http://www.fz-juelich.de/SharedDocs/Stellenangebote/_common/dna/2018-305-EN-PGI-2.html" target="_blank">See our webpage to apply</a><br />
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-8607803963879709362018-09-12T23:47:00.001-07:002018-09-12T23:51:57.827-07:00Postdoctoral research on Quantum Information and Thermodynamics<div dir="ltr" style="text-align: left;" trbidi="on">
Exact correspondences between seemingly different concepts play an important role in all fields of physics. An example is the fluctuation-dissipation theorem, which states that linear response of a system to external driving force corresponds to system fluctuations and this initiated important developments. Owing to technological miniaturization, nowadays quantum systems can be probed and controlled to high accuracy. However, theoretical efforts to identify quantum phenomena in thermodynamics are stalled by the difficulty of defining basic quantum quantities, such as heat flow, entropy production, work, and temperature. Recently using quantum information techniques Nazarov and Ansari developed a new correspondence in physics to extend the fluctuation-dissipation theorem into the realm of quantum systems.<br />
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To further study and test this new correspondence the theory group of Jülich-Aachen Research Alliance (JARA) at Peter Grünberg Institute in Germany is looking for highly motivated candidates to fill a postdoc position over the next few months.The project will be supervised by Dr. Ansari, and may involve collaborations with leading experimental groups. <br />
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Candidates with a PhD degree (or nearly graduating) in theoretical condensed matter physics or a related field can apply. Preference will be given to candidates with experience in background in quantum computation, condensed matter, statistical mechanics, and related topics, but strong candidates from other fields are encouraged to apply.<br />
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The application material should include:<br />
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• CV & transcripts <br />
• names & emails of 3 referees <br />
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If interested, please submit your files to m.ansari@fz-juelich.de. Review of applications will start in September and will continue until the position is filled.</div>
Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4070855.post-52784983500800924272018-07-08T06:23:00.001-07:002018-07-08T06:23:04.001-07:00Exact quantization of superconducting circuits<div dir="ltr" style="text-align: left;" trbidi="on">
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Another paper on transmon qubits is out. In this paper:</div>
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We present a theoretical description for circuits consisting of weak anharmonic qubits coupled to cavity multimodes. We obtain a unitary transformation that diagonalizes harmonic sector of the circuit. Weak anharmonicity does not alter the normal mode basis, however it can modify energy levels. We study two examples of a transmon and two transmons coupled to bus resonator, and we determine dressed frequencies and Kerr nonlinearities in closed form formulas. Our results are valid for arbitrary frequency detuning and coupling within and beyond dispersive regime. (M.H. Ansari)<div>
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<a href="https://scirate.com/arxiv/1807.00792" target="_blank">Full text</a> </div>
arXiv:1807.00792 <br /><div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-82069832260618384732018-04-09T12:17:00.002-07:002018-08-03T01:29:50.707-07:00Peter Grünberg<div dir="ltr" style="text-align: left;" trbidi="on">
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<a href="https://1.bp.blogspot.com/-GnND51umgGs/Wsu7u7agJYI/AAAAAAAA_Og/XwxiTpi5Cr4VLw9uvd6eg2WeGrLCjwqUQCLcBGAs/s1600/winner1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="233" data-original-width="350" height="213" src="https://1.bp.blogspot.com/-GnND51umgGs/Wsu7u7agJYI/AAAAAAAA_Og/XwxiTpi5Cr4VLw9uvd6eg2WeGrLCjwqUQCLcBGAs/s320/winner1.jpg" width="320" /></a></div>
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Our research institute is named after a 2007 Nobel Laureate: Prof. Peter Grünberg. Sadly I heard that Peter Grünberg passed away today. <br />
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Peter Grünberg in 1988 discovered giant magnetoresistance (GMR), for which in 2007 together with Albert Fert received the Nobel prize. <br />
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Their discovery allowed the storage capacity of hard drives to be significantly increased and made the miniaturization of storage devices. GMR is the sudden change in electrical resistance of a material, made of alternating ferromagnetic and non-magnetic metal layers, when exposed to large magnetic field. If magnetization of neighbouring layers is parallel, electrical resistance heavily drops, however if antiparallel the resistance goes much much higher. So this makes a large potential barrier between spin up and spin down, which can be used to code information on such a device. <br />
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-78732821973424975292018-01-11T12:12:00.000-08:002018-01-24T02:49:12.991-08:00Quantum Thermodynamics at APS March Meeting (2018)<div dir="ltr" style="text-align: left;" trbidi="on">
<br /><br />American Physics Society organises another March Meeting for a week this year again. The venue will be at Los Angeles. There is aninvited session on quantum thermodynamics and information that contains 5 interesting talk by experimental and theoretical physicists. Highly recommended!<br /><br />On Thursday morning 8-11AM, the following 5 invited speakers will give their talks:<br /><br /> Session R42: Progress in Quantum Thermodynamics<br /><a href="http://meetings.aps.org/Meeting/MAR18/SessionIndex2?tag=1">Invited</a> <br />Sponsoring Units: DQI GSNP<br />Chair: Mohammad Ansari, Forschungszentrum Julich<br />Room: LACC 502B <br /><br />8:00AM - 8:36AM<br />R42.00001: Progress in Thermodynamics of Superconducting and Hybrid Circuits<br />Invited Speaker: <b>Jukka Pekola</b> , Jonne Koski , Bayan Karimi , Alberto Ronzani , Jorden Senior , Olli Saira <br /><br />8:36AM - 9:12AM <br />R42.00002: Fluctuation Theorem for Many-Body Pure Quantum States<br />Invited Speaker: <b>Takahiro Sagawa</b> <br /><br />9:12AM - 9:48AM <br />R42.00003: Strong coupling quantum thermodynamics and beyond<br />Invited Speaker: <b>Q. Jens Eisert </b><br /><br />9:48AM - 10:24AM <br />R42.00004: Thermoelectrics of interacting nanosystems - Exploiting fermion-parity superselection instead of time-reversal symmetry<br /><br />Invited Speaker: <b>Janine Splettstoesser</b> , Jens Schulenborg , Joren Vanherck , Angelo Di Marco , Maarten Wegewijs <br /><br />10:24AM - 11:00AM <br />R42.00005: Quantum and Information Thermodynamics: A Unifying Framework Based on Repeated Interactions<br />Invited Speaker: <b>Massimiliano Esposito </b><br /><br />* By the way my own talk will be on the same day, an hour after this session is over, in another room. I'll give a talk about a new formalism to deal with Transmon-like qubits. More info can be found below:<br />
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<br /><a href="http://meetings.aps.org/Meeting/MAR18/Session/S39">Session S39: Superconducting Circuits: Modeling</a><br />11:15 AM–2:15 PM, Thursday, March 8, 2018<br />LACC Room: 501B<br />Sponsoring Unit: DQI<br />Chair: Antonio Corcoles, IBM T J Watson Res Ctr<br />12:15 PM–12:27 PM<br /><br />
Abstract: S39.00006 : Effective Hamiltonian in superconducting qubits<br /><b>Mohammad Ansari </b><br />(Forschungszentrum Juelich)<br /><br />Qubits with more than two energy levels, such as superconducting transmons, usually are externally driven in order to engineer one and two qubit gates. However due to the presence of higher excited levels the fidelity of the gates requires improvement. Such a system carries a large Hilbert space and recognizing effective qubits requires to use perturbation theory. This puts a lage limitation on the system parameters and interactions. We discuss a method that allows to go beyond regular perturbative limitations and separates classical effects from quantum fluctuations in the Hamiltonian of a weakly-anharmonic qubits. We compare results taken from applying Schrieffer-Wolff transformation, Least action principle, and our method. Our results will become practical tools for experimental efforts in circuit QED.<br />
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I may prepare a nice poster too to post on the wall, so please feel free to find my poster about a different topic:<br /><br />
#apsmarch<br /><br /><br /></div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-85687073779465468442017-10-16T06:54:00.003-07:002017-10-16T06:55:57.121-07:00Multiple PhD positions – JARA Institute for Quantum Information (RWTH Aachen & Forschungszentrum Jülich)<br />The theory groups at the Institute for Quantum Information of the Jülich-Aachen Reasearch Alliance (JARA) are looking for highly motivated candidates to fill multiple PhD positions over the next few months (a DFG-funded position could start as soon as possible). <br /><br />The doctoral projects will focus on theoretical studies of physical implementations of quantum information processing, such as superconducting and semiconducting qubits, and related enabling quantum technologies. The projects will be supervised by Dr. Ansari, Dr. Catelani, and/or Prof. Hassler, and may involve collaborations with leading experimental groups (IBM, Yale, Aalto, TU Delft).<br /><br />Master’s degree (or equivalent) in theoretical condensed matter physics or a related field and proficiency in English are required. Preference will be given to candidates with experience in quantum transport, superconductivity, and related topics, but strong candidates from other fields are encouraged to apply.<br /><br />The application material should include:<br /> <br /><ul>
<li>short letter of motivation ( </li>
<li>CV & transcripts </li>
<li>contact details (names & emails) of two possible referees </li>
</ul>
<br />For further information, or to submit an application, please contact one of us by email. Review of applications will start immediately and continue until all the positions are filled.<br /><br />Mohammad Ansari (<a href="mailto:m.ansari@fz-juelich.de">m.ansari@fz-juelich.de</a>)<br />Gianluigi Catelani (<a href="mailto:g.catelani@fz-juelich.de">g.catelani@fz-juelich.de</a>)<br />Fabian Hassler (<a href="mailto:hassler@physik.rwth-aachen.de">hassler@physik.rwth-aachen.de</a>)<br /><br /><br />Source: <a href="http://www.quantuminfo.physik.rwth-aachen.de/cms/Quantuminfo/Das-Institut/~drkm/Stellenangebote/?lidx=1">http://www.quantuminfo.physik.rwth-aachen.de/cms/Quantuminfo/Das-Institut/~drkm/Stellenangebote/?lidx=1</a><br /><br />Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-11236541066294542252017-05-20T08:17:00.003-07:002017-05-20T08:21:30.197-07:00Entropy production in a photovoltaic cell<div class="separator" style="clear: both; text-align: center;">
<a href="https://4.bp.blogspot.com/-advoRMZ6vy8/WSBeA2RSI1I/AAAAAAAAqvE/M4vID8oZaHE4M0eCjmDD2eTG_P-SNtWdwCLcB/s1600/Screen%2BShot%2B2017-05-19%2Bat%2B10.44.28.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="151" src="https://4.bp.blogspot.com/-advoRMZ6vy8/WSBeA2RSI1I/AAAAAAAAqvE/M4vID8oZaHE4M0eCjmDD2eTG_P-SNtWdwCLcB/s200/Screen%2BShot%2B2017-05-19%2Bat%2B10.44.28.png" width="200" /></a></div>
In the everyday world, the amount of disorder, or entropy, in an isolated system can only increase over time. This relation is described by the second law of thermodynamics. This indicates that not all of the energy we provide for a system can be converted into engineered work.<br />
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In quantum physics, however, the existence of such a law is obscure. One of the main reasons is that entanglement can dramatically alter the notions of disorder and equilibrium state. Instead of an analogue law, recently a correspondence has been found between entropy production and the statistics of energy transfers in a quantum system.<br />
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In my paper published recently at Physical Rev. B I studied how entropy is produced in a quantum heat engine. This helps us to explain how heat is dissipated in the engine. The engine is modelled by four electronic levels resonantly-coupled to thermal heat baths kept at different temperatures. Results show that quantum coherence that is induced by environment can significantly and nonlinearly modify entropy production in the cells. Consequently, the nonlinear entropy production can take place much slower or faster.<br />
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This determines under what conditions information in these cells can take a reversal flow from a cold to hot bath.<br />
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Ref: Mohammad H. Ansari, Phys. Rev. B 95, 174302 (2017)<br />
It is available online at <a href="https://doi.org/10.1103/PhysRevB.95.174302">https://doi.org/10.1103/PhysRevB.95.174302</a><br />
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<blockquote class="tr_bq">
<b>Abstract: </b><blockquote class="tr_bq">
I evaluate entropy production in a photovoltaic cell that is modeled by four electronic levels resonantly coupled to thermally populated field modes at different temperatures. We use a formalism recently proposed, the so-called multiple parallel worlds, to consistently address the nonlinearity of entropy in terms of density matrix. Our result shows that entropy production is the difference between two flows: a semiclassical flow that linearly depends on occupational probabilities, and another flow that depends nonlinearly on quantum coherence and has no semiclassical analog. We show that entropy production in the cells depends on environmentally induced decoherence time and energy detuning. We characterize regimes where reversal flow of information takes place from a cold to hot bath. Interestingly, we identify a lower bound on entropy production, which sets limitations on the statistics of dissipated heat in the cells.</blockquote>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-54955970117763751752017-04-15T21:13:00.002-07:002017-04-15T21:21:58.312-07:00Another PhD position is availableJob type: PhD<br />
Application deadline: Monday, June 5, 2017<br />
Employer: Peter Gruenberg Institute (PGI-2)<br />
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<a href="https://www.quantiki.org/position/phd-position-quantum-computing-and-physical-devices-germany" target="_blank">Another PhD position</a> is available to work at Peter Gruenberg Institute (PGI-2) and Juelich-Aachen Research Alliance Institute (JARA) in Forschungszentrum Juelich in Germany. The degree will be granted by RWTH University in Aachen. The student will work with Dr. Mohammad H. Ansari and the project can be started in the Summer or Fall 2017.<br />
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The purpose of the project is to develop relations between quantum computing models and physical devices. The project requires that you have basic knowledge of quantum physics and information, e.g. density matrix, decoherence, Bloch equation, correlations, nonequilibrium statistics, quantum information measures, Keldysh techniques, etc. We will collaborate with some theoretical and experimental research groups, such as the research group of Prof. D. DiVincenzo at PGI-2 and Prof. Y. Nazarov in Delft University of Technology.<br />
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For full consideration, please apply **as soon as possible** by sending your documents in *ONE pdf file* to "m.ansari AT fz-juelich.de", including:<br />
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1. your academic CV,<br />
2. your academic transcripts and the list of publications,<br />
3. a short essay relating your knowledge to recent papers written by Dr. Ansari (no more than 300 words ~ two paragraphs)<br />
4. the names, affiliation, and email addresses of 2 or 3 referees, (make sure they are willing to send letters on time)<br />
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Please make sure to choose the following subject for your email: "Ph.D. position at PGI-2"<br />
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More updates about the position can be found at: https://sites.google.com/site/mansariUnknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-72658155763587803152017-03-27T15:10:00.002-07:002017-03-31T04:34:12.522-07:00My talks on Entropy-Noise Correspondence<div class="separator" style="clear: both; text-align: center;">
<a href="https://2.bp.blogspot.com/-0fPWUtCCtaE/WNmIlDKP8mI/AAAAAAAAm38/YkggVH4Sh0QR4k0N67Q5f922Tf5b3mY_ACLcB/s1600/huckleberry_finn_015_jpg_fedu.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="218" src="https://2.bp.blogspot.com/-0fPWUtCCtaE/WNmIlDKP8mI/AAAAAAAAm38/YkggVH4Sh0QR4k0N67Q5f922Tf5b3mY_ACLcB/s320/huckleberry_finn_015_jpg_fedu.jpg" width="320" /></a></div>
I am back from a loooong long trip into several cities in the US and Canada, where I gave a series of talks about my research. <br><br>
In my trip to New Orleans, for the first time I saw real palm trees! The city has its own character within its cheesy streets full of excited visitors and free storytelling stations! I was also excited to see Mississippi river, which reminded me one of the cartoons I was watching when I was almost ten: the Adventures of Huckleberry Finn! At APS March meeting I enjoyed meeting some old friends from Japan, the US, Canada, Germany, Holland, Australia, etc, gave a short talk about "information contents of physical interactions" and enjoyed learning new things. <br><br>
Later I traveled to Canada to give a series of talk in different places and to visit a research group for future collaborations. My schedule was very rich! I started with the University of Toronto, then went to Waterloo to visit and give a talk at the Institute for Quantum Computation (<a href="http://iqc.ca">IQC</a>) on how to measure entropy in quantum systems. <a href="https://uwaterloo.ca/institute-for-quantum-computing/events/seminar-mohammad-ansari">+</a> <br><br>
As planned I also visited the Perimeter Institute in Waterloo too, where I got my PhD degree 9 years ago from within its old building, the post office building. The "new" building has changed a lot and now has a wired wing full of offices to somehow compensate its original land-wasting floor map. There were too many new faces there and almost nobody recognised me except a few of present faculty members. There I gave a talk in the quantum foundations seminars about the new entropy-noise correspondence we found last year <a href="http://www.perimeterinstitute.ca/seminar/entropy-measurement-quantum-systems">+</a> <br><br>
These talks turned out to fall into the interest of two main communities: condensed matter theorists and quantum information theorists. <br><br>
To provide equal opportunities to those not present in the cities yet like to form and express a judgement, I uploaded <a href="https://www.dropbox.com/s/8zelb8kz2vkuwqp/MAnsariPublic1.pdf?dl=0">a short summary of my presentations here to be accessible to public</a>. Please feel free to review. <br><br>
M.H. Ansari Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-55590746484996063952017-03-05T23:26:00.002-08:002017-03-05T23:26:28.084-08:00Talks<br />If you happen to be near Aachen this week, come to hear news about entropy. (<a href="http://www.quantuminfo.physik.rwth-aachen.de/go/id/fwck/lidx/1" target="_blank">this link</a>) <div>
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***********************************************************<br />Quantum information seminar, Mar 09 11:00, Physikzentrum MBP2 116<br />***********************************************************</div>
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SPEAKER: Mohammad Ansari (FZ Jülich)<br />TITLE: Entropy measurement in quantum systems<br /><br />ABSTRACT: Entropy is an important measure of information. Being nonlinear in density matrix, its consistent evaluation for a quantum system requires a formalism that allows simultaneous evolution of more-than-one-copy of density matrix. Recently in [MHA and Y. Nazarov, Phys. Rev. B 91, 104303 (2015)] a formalism for such evolutions has been proposed and [MHA and Y. Nazarov, Phys. Rev. B 91, 174307 (2015)] shows that such entropy correspond to physical quantities. Interestingly this correspondence is not equivalent to the second law of thermodynamics. In this talk I describe how to measure entropy flow in a quantum heat engine.<br /><br />************************************************************</div>
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Also next week I am in New Orleans. If you are attending APS March meeting I am going to give a talk in <a href="http://meetings.aps.org/Meeting/MAR17/Session/L52">Session L52: Statistics of Ensemble Quantum Systems</a> Wednesday at 11:50 AM in Room: 399. </div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-73033660178899532342017-02-01T03:27:00.000-08:002017-02-03T05:12:37.535-08:00A postdoc/PhD student positionA fully-funded <a href="https://quantiki.org/position/postdocphd-student-position-germany" target="_blank">postdoc/PhD student position</a> is available to work at Peter Gruenberg Institute (PGI-2) in Forschungszentrum Juelich, near Aachen in Germany. For students the degree will be granted by RWTH university in Aachen. The researcher will work with Dr. Mohammad H. Ansari. The project can be started in the Summer or Fall 2017.<br />
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The purpose of the project is to develop the relations between quantum information theory and physics. For this aim we recently developed a new formalism called multiple parallel world technique. Our findings will be used to explore new phenomena in quantum computing, thermodynamics, and photosynthetic complexes in biology. The project requires that you have basic knowledge about quantum physics and information, e.g. density matrix, decoherence, Bloch equation, correlations, nonequilibrium statistics, quantum information measures, Keldysh techniques, etc.<br />
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We will collaborate with some theoretical and experimental research groups, such as the research group of Prof. D. DiVincenzo in PGI-2 and Prof. Y. Nazarov in Delft University of Technology, the Netherlands, et. al. The employed researcher will have the opportunity to visit our collaborators.<br />
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Everyone (Masters and PhD students and Postdocs) from all around the world are welcome to apply.<br /><br />For full consideration, please apply as soon as possible, by sending your documents in *ONE pdf file* to "mansari AT gmail DOT com", including:<br /><br />1. your academic CV,<br />2. your list of publications,<br />3. research interests on what makes your past research experience related to quantum thermodynamics, (no more than 300 words ~ two paragraphs)<br />4. the names, affiliation, and email addresses of 2 or 3 referees, (make sure they are willing to send letters on time)<br /><br />More information about the research details as well as announcements (e.g. whether the position is still available or not) can be found at:<br /><a href="https://sites.google.com/site/mansari">https://sites.google.com/site/mansari</a><br />
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-46292582598394817652016-11-30T06:27:00.002-08:002016-12-05T08:33:50.500-08:00A newly-published course book by Manoukian<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-vk7NOscHkXs/WD7lUofJikI/AAAAAAAAhKQ/EPsJs_Z-xg4OAZPLzFX-BzfTAGthyS89wCLcB/s1600/41gC90fwbvL._SX330_BO1%252C204%252C203%252C200_.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="https://3.bp.blogspot.com/-vk7NOscHkXs/WD7lUofJikI/AAAAAAAAhKQ/EPsJs_Z-xg4OAZPLzFX-BzfTAGthyS89wCLcB/s320/41gC90fwbvL._SX330_BO1%252C204%252C203%252C200_.jpg" width="212" /></a></div>
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December this year is almost the 10th anniversary of finding new degeneracy in area spectrum and finding heir application. (<a href="https://arxiv.org/abs/gr-qc/0603121" target="_blank">1</a>,<a href="https://arxiv.org/abs/hep-th/0607081" target="_blank">2</a>)<br />
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Yesterday I was informed in an email from Springer that some of those results about area quantization have found their way into a newly-published graduate textbook. Although this is not the first time that somebody writes about what I have done (see footnotes) but this time feels differently because my physics is now a part of a graduate course book.<br />
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<a href="https://www.amazon.com/Quantum-Field-Theory-Introductions-Supersymmetry/dp/331933851X/ref=sr_1_1?s=books&ie=UTF8&qid=1480516424&sr=1-1" target="_blank">Here</a> is the book: "Quantum Field Theory II: Introductions to Quantum Gravity, Supersymmetry and String Theory (Graduate Texts in Physics.) written by E.B. Manoukian and published by Springer on September 2016).</div>
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I read some parts of it, yet not all, and to my point of view it is quite decent book in the field, well-written and organized, and clear. It provides interesting insights about recent developments in quantum field theory. More importantly it teaches how modern physicists think about quantum foundations, overall a must-read book for graduate students working on quantum field theory.<br />
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This is pretty exciting to see that the degeneracy of quantum area spectrum and its physical applications ten years after its discovery are now exercises for young students!<br />
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Footnotes:<br />
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* D. Oriti, Approaches to Quantum Gravity: Toward a New Understanding of Space, Time and Matter (Cambridge University Press 2009) highlighted my research on black hole and area quantization.<br />
<img src="file:///page2image34552" /> <img src="file:///page2image34712" /> <img src="file:///page2image34872" /> <img src="file:///page2image35032" /> <img src="file:///page2image35192" /> <img src="file:///page2image35352" /> <img src="file:///page2image35512" /> <img src="file:///page2image35672" /> <img src="file:///page2image35832" /> </div>
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* M. Aschwanden, Self-Organized Criticality in Astrophysics: The Statistics of Nonlinear Processes in the Universe (Springer London 2011) highlighted my research on cellular automata, self-organized criticality and nonequilibrium phenomena.<br />
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* A section 2.46.3 of the book: The Cosmic Compendium: Black Holes by R. W. Anderson has devoted only to explain my results on black hole.<br />
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* The article by L. Smolin, in Physics Today 59 Nov 44 (2006) highlighted some of my results on black holes <a href="http://dx.doi.org/10.1063/1.2435646">http://dx.doi.org/10.1063/1.2435646</a> , etc.</div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-16561268265113082082016-05-17T13:11:00.001-07:002016-06-09T02:00:42.218-07:00News about entropy<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-FBIwPX-ZwNg/V1ktmguRTiI/AAAAAAAAYqI/jWUGr5tordwxmLMt9iTDgDRtaYm0iUmXACLcB/s1600/Shannon_Entropy.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://3.bp.blogspot.com/-FBIwPX-ZwNg/V1ktmguRTiI/AAAAAAAAYqI/jWUGr5tordwxmLMt9iTDgDRtaYm0iUmXACLcB/s1600/Shannon_Entropy.jpg" /></a></div>
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Did you know that you have been calculating entropy incorrectly during your whole life! This is at least what I claim to be true in a recently published paper titled: "A consistent flow of entropy."<br />
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A common approach to evaluate entropy in quantum systems is to solve a master-Bloch equation to determine density matrix and substitute it in entropy definition. However, this method has been recently understood to lack many energy correlators. The new correlators make entropy evaluation to be different from the substitution method described above. The reason for such complexity lies in the nonlinearity of entropy. In this paper we present a pedagogical approach to evaluate the new correlators and explain their contribution in the analysis. We show that the inherent nonlinearity in entropy makes the second law of thermodynamics to carry new terms associated to the new correlators. Our results show important new remarks on quantum black holes. Our formalism reveals that the notion of degeneracy of states at the event horizon makes an indispensable deviation from black hole entropy in the leading order.<br />
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This is a my contribution to special issue in Fortschritte der Physik for the Frontiers of Quantum and Mesoscopic Thermodynamics Conference. Link: <a href="http://arxiv.org/abs/1605.04620">arXiv:1605.04620</a><br />
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By: Mohammad H. Ansari</div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-51719547922438654142016-02-11T14:16:00.000-08:002016-02-17T15:23:55.226-08:00Hearing a sound from a billion years ago!<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-jxoFsc4ewA8/Vr0HyPvHDdI/AAAAAAAAT3Q/XaGJopfhLSs/s1600/2-black-holes-gravitational-waves.jpg" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="200" src="https://3.bp.blogspot.com/-jxoFsc4ewA8/Vr0HyPvHDdI/AAAAAAAAT3Q/XaGJopfhLSs/s200/2-black-holes-gravitational-waves.jpg" width="200" /></a></div>
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Today is a day for cheering. After many years gravitational waves have been finally reported to have been detected. In two separate detectors, in west and east coasts of the US, almost simultaneously it was detected that earth got shrunk a tiny bit from a gravitational curving pulse. Many researchers have been sweating for decades to make these detectors happen.<br />
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Let me explain what has been discovered. An early approval for the theory of general relativity in 60's was based on the following fact: the presence of a heavy object, like our sun, will causes its surrounding spacetime to be curved. This has been observed from the following experiment: the straight path on which light travels in the universe from A to B, if passes adjacent to a heavy object, will bend a bit toward the object, thus the path will not remain a straight path anymore.<br />
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Now, consider two heavy objects crazily rotate around one another with a crazy speed (a half of speed of light). Right before they merge they make a lot of ups and downs in the spacetime in between. This turbulence in the very spacetime fibres propagate to others places, similar to how tsunami waves propagate in the ocean. In other words, gravitational field is self-interacting; this means that it sources itself. It curves the space around itself because it carries mass/energy by itself much like a star does.<br /><br />If the objects are many light years away, the waves passing through the Earth today makes a bit of stretches and squeezes in the radius of earth, something of the size of less than the radius of proton! This has been detected last year at LIGO detectors and today was reported, and peer reviewed already in the <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102" target="_blank">PRL</a>.<br />
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From what they received we assume that the waves came from two 30-solar-mass black holes curling up around one another in a death spiral, a billion light-years away from us. This is a better-than-expected source for LIGO and sometimes the universe is nice to us! In fact a billion years ago two heavy stars fell in love with one another and played hand in hand like kids, and today we got a bit of <a href="https://www.youtube.com/watch?v=TWqhUANNFXw" target="_blank">their happy sound</a>! Doing such an amazing science is similar walking a tightrope between surly curmudgeon and starry-eyed cheerleader. </div>
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The last thing to notice: If you are sad you do not get cited more often, apparently Einstein’s prediction of gravitational waves has been cited <a href="http://adsabs.harvard.edu/abs/1916SPAW.......688E" target="_blank">only a few times</a>! <br />
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By: Mohammad H. Ansari</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-86096170472049237092016-01-25T08:30:00.003-08:002016-06-09T01:52:48.970-07:00APS March Meeting 2016<div class="separator" style="clear: both; text-align: center;">
<a href="http://4.bp.blogspot.com/-QjgewuEc_Vw/VqZORuOSk3I/AAAAAAAATIY/9XJkFIkqAcA/s1600/Screen%2BShot%2B2016-01-25%2Bat%2B17.31.53.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="139" src="https://4.bp.blogspot.com/-QjgewuEc_Vw/VqZORuOSk3I/AAAAAAAATIY/9XJkFIkqAcA/s200/Screen%2BShot%2B2016-01-25%2Bat%2B17.31.53.png" width="200" /></a></div>
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I'll be chairing a session in the upcoming American Physics Society March Meeting 2016 in Baltimore, USA. The session is focused on Quantum Information and Thermodynamics.<br />
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Below you can find the session information. I invited some notable young scientists whose contribution to quantum physics have been impressive in the last year.<br />
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Looking forward to run an impressive focus session!<br />
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<a href="http://meetings.aps.org/Meeting/MAR16/Session/R44">http://meetings.aps.org/Meeting/MAR16/Session/R44</a><br />
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Mohammad H AnsariUnknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-89412449745914003442015-12-24T02:53:00.003-08:002015-12-25T19:12:24.495-08:00Abdolali Ansari 1931-2015<a href="http://4.bp.blogspot.com/-Wad-4cd8ikE/VnvKoUXlO5I/AAAAAAAAR5o/LxOxWXkD4dc/s1600/IMG_4891.JPG" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="240" src="http://4.bp.blogspot.com/-Wad-4cd8ikE/VnvKoUXlO5I/AAAAAAAAR5o/LxOxWXkD4dc/s320/IMG_4891.JPG" width="320"></a><br>
My father passed away yesterday 22 Dec 2015 after a rather short period of age-related illness. He was 84. My father, Abdolali, was a college president and teacher in Kermanshah. He spent most of his efforts to boost up the education quality of the college Daneshsaraa-ye Aali of Kermanshah (college for teacher training). Sometimes, only for joy of it, he contributed to teach geometry, mathematics, and literature. He loved to share his knowledge with his pupils.<br>
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Before joining the college he has experienced many other activities such as the business of Giveh, a traditional type of footwear woven by silk and cotton for daily use in western Iran. Nowadays this business is in the hand of my uncles. At age 20, not satisfying from business, he passed an exam and was accepted to enter medical school in Tehran. After a short time he decided to change the field into science educational school for which he and his family of wife and two daughters moved to Tehran. Four years later he received the degree from one of the best universities in tehran and moved back to Kermanshah to help establishing a modern college named Daneshsaraa-ye Aali of Kermanshah, he was president of the college for more than 20 years.<br>
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On weekends of my intermediate school days, one of my best hobbies was to go beyond the geometry of school books. I had a wonderful teacher at home playing with the roses and other flowers of our house yard. I was going to him asking whether he likes to teach me and his response was always with a flame of joy in his eyes. Sometimes we were working more than 5 hours together on different aspects of mathematics, I was sitting next to him working on paper with compass, set square, protractor, drawing lines and curves for proving theorems he was assigning to me. On top of methods, such as how to partition an angle into three with compass, the joy of discovery was what I learned the most from him.<br>
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After retiring from the college, he started a new career at Razi University in Kermanshah shortly before our entire family move to Tehran. In Tehran, he started another careers in finance, working everyday until the age of 75, not that he needed, only because he loved to work. At this age he started to reduce his activities and stayed mostly at home, yet he was still the source of hope for us. In all ups and downs when I was sharing what is in my chest to him, he could sparkle my mind with the burst of a wise word. This was what I needed to be cheered up. <br>
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Abdolali Ansari left behind thousands of students some of whom are nowadays the most influential people in their profession.<br>
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God bless you daddy. I am happy that you are eternally home. God bless you...<br>
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<div id="fb-root"></div><script>(function(d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) return; js = d.createElement(s); js.id = id; js.src = "//connect.facebook.net/en_US/sdk.js#xfbml=1&version=v2.3"; fjs.parentNode.insertBefore(js, fjs);}(document, 'script', 'facebook-jssdk'));</script><div class="fb-post" data-href="https://www.facebook.com/mhhansari/posts/10153905844176995" data-width="500"><div class="fb-xfbml-parse-ignore"><blockquote cite="https://www.facebook.com/mhhansari/posts/10153905844176995">Posted by <a href="#" role="button">Mohammad H. Ansari</a> on <a href="https://www.facebook.com/mhhansari/posts/10153905844176995">Thursday, December 24, 2015</a></blockquote></div></div>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-33621339690447727642015-09-15T02:59:00.000-07:002016-06-09T01:54:25.181-07:00Let's move to physical quantities: Keldysh Green functions!<div>
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<a href="https://4.bp.blogspot.com/-UGCglYLcL4E/V1kurr1aTpI/AAAAAAAAYqU/XcTmremkvYcrCehX09T9HFph43lkixGvgCLcB/s1600/Nazarov_405.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://4.bp.blogspot.com/-UGCglYLcL4E/V1kurr1aTpI/AAAAAAAAYqU/XcTmremkvYcrCehX09T9HFph43lkixGvgCLcB/s1600/Nazarov_405.jpg" /></a></div>
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Yuli Nazarov: [I] remember a talk given by a high-class theorist with a taste for abstract models, young experimentalists being his primary audience. Somewhere in the middle of the talk he said: "Now let us move to physical quantities, namely, Keldysh Green functions". A burst of laugh lasted for more than five minutes!</div>
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For many years Keldysh formalism was considered too much complicated for a practical researcher and hardly applied beyond several specific fields. "Keldysh approach" sounded as a synonym of unnecessary theorization and an antonym to clear physical reasoning.<br />
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<br />
Excerpts from:</div>
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<br />
<b>Keldysh formalism for multiple parallel worlds</b></div>
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Abstract: <br />
We present here a compact and self-contained review of recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to evaluation of Renyi and Shannon entropy flows. We start with the formulation of standard and extended Keldysh technique in single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds In the end, we shortly summarize the concrete results obtained with the method.<br />
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Mohammad Ansari and Yuli V. Nazarov<br />
<a href="http://arxiv.org/abs/1509.04253">arXiv/1509.04253</a></div>
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<br />
(Submitted on 14 Sep 2015)<br />
<br />
It is a big honour for us to present these results in a special issue celebrating numerous
scientific merits of Leonid Veniaminovich Keldysh. We gladly appreciate his pioneering research that provided a powerful and indispensable tool for many generations of quantum
physicists, us including, and wish him many happy returns of the day.</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-82034074322709882932015-08-19T22:56:00.001-07:002016-03-01T11:28:49.325-08:00Early look at CQI sessions in APS March meeting 2016I'll be organizing a focus session for CQI on Quantum Information and Thermodynamics in the APS March meeting 2016 in Baltimore. The submission of abstract will becomes available in September. Experimentalists and theorists please consider to submit your abstracts to the session, or introduce it to your colleagues. For any question please feel free to contact me.<br />
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<b>Focus Topics (see descriptions below) </b><br />
<div>
Towards Scalable Quantum Computers <br />
Hybrid Quantum Systems <br />
Adiabatic Quantum Computation and Quantum Annealing <br />
Finite-size Quantum Information Theory <br />
Quantum Characterization, Validation, and Verification <br />
Quantum Information and Thermodynamics <br />
Gravity and Quantum Information <br />
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<b>Regular Sorting Topics </b><br />
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Superconducting quantum information <br />
Semiconducting quantum information <br />
Atomic, molecular and optical (AMO) quantum information <br />
Topological quantum information <br />
Algorithms and architecture for quantum information <br />
Quantum information theory and quantum foundations <br />
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<b>Abstracts:</b></div>
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<br />
<b>Towards Scalable Quantum Computers</b><br />
This focus topic will examine recent advances towards scalable quantum information devices. The topic will include experimental talks on both solid state and AMO qubit technologies with an emphasis on improved gate fidelities and the development of integrated systems. It will also include theoretical talks on improvements in quantum error correction, quantum control, and proposals for scalable architectures.<br />
<br />
<b>Hybrid Quantum Systems</b><br />
This focus topic will examine recent experimental and theoretical developments in hybrid quantum systems that combine quantum system of multiple types. Examples range from quantum dots coupled to microwave cavities to trapped ions coupled to micromechanical resonators.<br />
<i>Organizer: Guido Burkard, University of Konstanz </i><br />
<b><br /></b>
<b>Adiabatic Quantum Computation and Quantum Annealing</b><br />
Adiabatic models of quantum computation and quantum annealing perform computational tasks by evolving the system under a slowly changing Hamiltonian. This topic will focus on the theory and applications of adiabatic quantum computers and quantum annealers, and challenges for error suppression and correction on these devices.<br />
<i>Organizer: Daniel Lidar, University of Southern California</i><br />
<b><br /></b>
<b>Finite-size Quantum Information Theory </b><br />
A growing topic of interest in quantum information theory is to understand what the capabilities are for a finite number of quantum systems. Traditionally, the focus has been on asymptotics and there has been a disconnect between the theory and what is possible in practice. In the past three years, the theoretical tools have sharpened significantly and we can answer questions such as "How many qubits can I send with 100 channel uses if I desire an error probability no larger than 10-6 ?" Answers to such questions place fundamental limitations on small quantum computers and are the focus of this session.<br />
<i>Organizer: Mark Wilde, Louisiana State University</i><br />
<b><br /></b>
<b>Quantum Characterization, Validation, and Verification</b><br />
As reported errors in quantum gates approach fault-tolerance thresholds, it becomes more important to confirm the methods by which errors are assessed and gate functions are determined. This topic will include recent advances in tomography and benchmarking methods, tests for detecting coherent errors, and appropriate error bounds for quantum error correction.<br />
<i>Organizer: Charles Tahan, Laboratory for Physical Sciences, University of Maryland</i><br />
<b><br /></b>
<b>Quantum Information and Thermodynamics</b><br />
It is increasingly apparent that quantum entanglement offers a powerful tool to describe physics. This is necessary to develop realistic proposals for measuring entanglement as well as other quantum information quantities from physical quantities. In the past decade, owing to the control of small-scale devices such as quantum heat engines and electronic circuits, thermodynamics has become part of the bedrock to understand how to measure information quantities in the physical world. Establishing thermodynamics in quantum scales requires a quantum description for exchange of physical quantities such as energy, charge, spin, etc. This requires generalization of information correlations that sometimes goes beyond standard definitions for entanglement. These correlations in condensed matter and information theory have been realized and are the driving force behind recent developments.<br />
<i>Organizer: Mohammad Ansari, TU Delft</i><br />
<b><br /></b>
<b>Gravity and Quantum Information</b><br />
Quantum information is providing a fresh look at the gravity-quantum interface. Experiments range from high-precision measurements of the gravitational field using quantum systems all the way to actual large quantum superposition states of clocks or increasingly massive objects, where experiments may be in reach in the near future. In addition, the relevance of quantum information concepts for studying fundamental properties of space-time.<br />
<br /></div>
</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-29980737125172008332015-08-17T16:14:00.000-07:002016-03-02T10:10:39.136-08:00My memory of Jacob Bekenstein<div>
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Jacob Bekenstein passed away at age 68. I know Jacob mostly from reading his papers on gravity and information theory, but I also have had an interaction with him about physics.<br />
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He was a brilliant scientist who will be missed in the community of quantum gravity. He had great contribution to the thermodynamics of black holes and its entropy, known as the Bekenstein entropy. </div>
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The original thought he had relies on an assumption that the information may be organized into binary digits on the black hole horizon where information exchange with black hole interior region (in his view) stops. This idea although is very heuristic, but motivated further investigates, without which it would take long time before thermodynamics of black holes is found. </div>
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<div class="p1">
<span class="s1">Since then there have been many attempts to calculate the black hole entropy. For example, in one of the most recent attempts Ashtekar, et.al showed that from writing the action of spacetime dynamic in terms of gauge fields, the associated action to a black hole horizon becomes the Chern-Simons action. Quantization will end up in some punctures on the horizon, which carry degenerate states. Other arguments for similar derivation has been made much earlier in string theory by Vafa et. al. </span></div>
<div class="p1">
<br /></div>
</div>
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Now, let me go back to the story between me and Jacobe Bekenstein. In 2007 I was a third year PhD student at the Perimeter Institute in Canada working on black holes. I have just published two solo-author long papers in Nuclear Physics B (<a href="https://scholar.google.ca/citations?view_op=view_citation&hl=en&user=Wlg2a9AAAAAJ&citation_for_view=Wlg2a9AAAAAJ:u5HHmVD_uO8C" target="_blank">this</a> and <a href="https://scholar.google.ca/citations?view_op=view_citation&hl=en&user=Wlg2a9AAAAAJ&citation_for_view=Wlg2a9AAAAAJ:u-x6o8ySG0sC" target="_blank">this</a>) where in I discussed the full spectrum of area operator in loop quantum gravity carries an internal degeneracy. The longer paper was first discussing an explicit mathematical proof to show the full spectrum of area no matter in what gauge representation is made of infinite number of equidistant subsets. Moreover, Jacobe Bekenstein and Viatcheslav Mukhanov (BM) have earlier argued based on the heuristic area quantization that black holes must radiate an evenly spaced spectrum of photons on top of Hawking radiation. The explicit quantization of area modified this result. Although it supports that a black hole radiates photons of discrete energies, however it predicts that, despite what BM predicts, the energy spectrum is not evenly spaced and that if one can detect at least three of the frequency lines it determines the internal gauge symmetry of the universe. </div>
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<br /></div>
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For these works I received the John Brodie prize and was nominated for a fellowship at Harvard which was almost hopeless to get in the presence of a nasty war in the blog sphere flaming between string theorists and those who take different approach, similar to that of Bekenstein's. Students were the first victims of this unnecessary hurlyburly. </div>
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Anyways, let me go back to the story. On a cold Suday morning of Canada in Nov 2007 when I woke up into the warm radiation of sun spreading in front of my little window in Waterloo, I checked my emails and to my absolute surprise I saw an email from "Jacobe Bekenstein" among my messages, which first I thought it must be fake. When I opened it up I saw it is from himself cc-ed to Viatcheslav Mukhanov. I read it and was shocked in the honour. Jacobe has already read my papers and prepared some comments on it. He started his rather long letter with:<br />
<div>
<br /></div>
"Dear Dr. Ansari,<br />
<br />
<div>
Your paper on loop quantum gravity's predictions for the black hole area spectrum is interesting...<br />
Although you find another series of levels that are not equidistant, you correctly argue that the<br />
transitions between equidistant ones will prevail in the radiated spectrum. From an "observational" point of view, the equidistant levels are all that matters.<br />
..."<br />
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<br /></div>
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He continued his letter with 4 important comments that helped to improve my papers and the history of proper references. I was a bit in shock to see that one of my heros in quantum information and gravity initiated writing such a descriptive letter to a random PhD student with such an exquisite accuracy of equation numbers and pages. </div>
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In a few days I responded to him, cc-ed to Mukhanov: </div>
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<br /></div>
"Dear Professor Bekenstein,<br />
<br />
It is a pleasure that I read your valuable comments. Thank<br />
you for your message. I was not aware of the history of this line of<br />
research to this depth. Previously, I enjoyed a discussion with Prof. Mukhanov<br />
on this topic in a talk I gave a while ago at the Perimeter<br />
Institute. I will read and study the references you mentiond and also<br />
in the next version of the paper I will give the information to<br />
readers and put enough stress on the origins of the methods.<br />
..."<br />
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<div>
<br /></div>
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Then I explained some technical details about the work and explaining how different is the spectrum of loop quantum gravity from that of his. At the end, I asked him the following question: </div>
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<br /></div>
"I am very interested to see the possibility of observing these lines (evenly-spaced, or unevenly-spaced ones). Do you have any estimate about the possibility of their detections. Some recent work suggest that they should potentially been detectable in INTEGRAL observations etc." <br />
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In response he wrote:</div>
<br />
"... Regarding the observability of the lines (in whatever scheme, yours, or ours) the problem will<br />
always be astrophysical radiation background. Usually lines of interest can be picked up if one knows a priori their frequencies. Here one does not because the mass of the hole could be anything."<br />
<br />
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Although I did not see Jacobe and do not know him in person, but these short communication helped me to see that one can be a great mind and at the same time not reluctant to learn from a nobody junior scientist. </div>
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<br /></div>
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Mohammad H. Ansari<br />
<br /></div>
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</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4070855.post-6050574069927026772015-07-15T00:41:00.003-07:002015-07-15T01:15:56.052-07:00Stimulated quantum phase slips<div>
Stimulated quantum phase slips from weak electromagnetic radiations in superconducting nanowires,<br />
<a href="http://arxiv.org/abs/1507.02725">arxiv.org:1507.02725</a><br />
Amir Jafari-Salim, Amin Eftekharian, A. Hamed Majedi, Mohammad H. Ansari<br />
<br />
<div>
<br /></div>
This paper is on radiation-assisted quantum phase slip. We study the rate of quantum phase slips in an ultranarrow superconducting nanowire exposed to weak electromagnetic radiations. The superconductor is in the dirty limit close to the superconducting-insulating transition, where fluxoids move in strong dissipation.<br />
<br />
We use a semiclassical approach and show that external weak radiation exposed to an ultranarrow superconducting nanowire at low temperature stimulates a significant enhancement in the probability of quantum phase slips in the wire. This can help to outline a new type of detector for microwave to submillimetre radiations based on stimulated quantum phase slip phenomenon.</div>
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<br />Unknownnoreply@blogger.com0