# ƒڊ֌WZ~i[́Aȉ̂RłF

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## Seminars hosted by Shimizu Lab.

Open to all researchers and students!
No application is necessary.

access and map

2016/11/8 (Tu) 10:10-11:50, room 829,  8F of Building 16, Komaba I campus, The University of Tokyo.

 Speaker (1) q icmwHwj60 minutes including discussion(2) Members of Shimizu lab. 5 minutes each including discussion Title (1) _ChdqXspʎqZVO(2) Current studies in Shimizu lab. Abstract (1) ߔNC̒2ʌn̗ʎqRq[X𗘗pʎqEʎqvɊւ錤ɍsȂĂDȂł_Ch̒fESiNVSjSɋǍ݂dqXsԂ́CɂĒXsRq[XԂL邱ƁC}CNgpEEǂݏoeՂł邱ƂCxEԕ\LʎqZTւ̉p҂ĂDNVSpʎqZT邽߂ɂ́C̗ǂ䂳ꂽNVS̐ZpƂƂɁCdqXsԂxɗʎq䂵Ȃ玥C𑪒肷邽߂̌oCJ邱ƂdvłD{\ł́C׉HƉwCiCVDj@gݍ킹V@ɂʒuEz䂳ꂽNVS̐ƓɊւX̌ʂЉƂƂɁCXJxoC̊TvƓdqXsRq[Xp𗬎ZVOɊւŋ߂̉X̐ʂЉD

2016/10/20 (Th) 10:00-16:00, room 121, Building 3, Komaba I campus, The University of Tokyo.

 Speaker t i{wpUʌPDj Title ÓTv͊w̗jIWJFATu_𒆐S Abstract @v͊w̗jUԂƂC͏Ƀ}NXEF{c}̖ɌyD͌Čł͂ȂDނ͕wɊmz݁CĈ̐UTCM͊w@̓o߂ĉ؁X_JLD̂ƂɂĂ͏ڂDC΂΁iÓTjv͊ẘ҂ƂČMuXɂĂ͂ǂ낤H@̃Z~i[ł́C܂j̎@ЉCʏ铝v͊w̗jmFĎCu҂̊֐SłMuX̃ATu_̌ƎeɂāC̌ʂqׂB

2015/04/09 (Th) 11:00-16:30, room 202 (Shimizu Lab. room), Building 16, Komaba I campus, The University of Tokyo.

 Speaker Prof. Tobias Brandes (Technische Universitat Berlin, Institut fur Theoretische Physik) RɎq iM2j Title A Special Seminar with OHANAMI iԌj Lunch Program 11:00-13:00 : OHANAMI iԌj with lunch13:00-14:00 : Talk (incl. discussions) by Ryoko Hatakeyama: Quantum Thermodynamic Machines14:00-14:30 : Coffee14:30-15:30 : Talk (incl. discussions) by Prof. Brandes : Feedback Between Interacting Transport Channels15:30-16:30 : Coffee and genearal discussions

2015/1/21 (Wed) 14:50-16:00, room 410, Advanced Research Laboratory, Komaba I campus, the University of Tokyo.

ɂĂ̒ӁF Or[̋߂ɂAdvanced Research LaboratorŷSK̑c(410jłǍ̓́AGgXJ[hȂƓ܂BO炨ź̕Ai162K202jɗȂǂāA̋wƈꏏɂꉺB

 Speaker n I iUniversity of California, Berkeleyj Title Time crystal̎s\ (Absence of Quantum Time Crystals) Abstract ԕiΏ̐Iɔjʏ̌Ƃ̃AiW[ŁAߔNFrank Wilzeck͎ԕiΏ̐j"time crsytalhA܂uԕւ̌vƂVԂĂB̗_IĂ͂̎\ɊւėlXȋc_Ă񂾂A̋c_ɂĂtime crystal̒̂BɂȂĂƂ肪BX́A܂Ԉˑ֊֐ptime crystal̒ĂÂ悤ɒꂽtime crystalHamiltonian̋Ǐv葶݂ȂƂʓIɏؖBIn analogy with crystalline solids around us, Wilczek recently proposed the idea of "time crystals" as phases that spontaneously break the continuous time translation into a discrete subgroup. The proposal stimulated further studies and vigorous debates whether it can be realized in a physical system. However, a precise definition of the time crystal is needed to resolve the issue. Here we first present a definition of time crystals based on the time-dependent correlation functions of the order parameter. We then prove a no-go theorem that rules out the possibility of time crystals defined as such, in the ground state or in the canonical ensemble of a general Hamiltonian, which consists of not-too-long-range interactions.nӂ̂ӂŁAZ~i[̃XChɂ܂B

F@t@Z~i[ ij

2013/6/13 (Th) 13:30-17:30, room 129, Building 16, Komaba I campus, the University of Tokyo.

(Will be extended, if necessary, to 6/14 (Fr))

 Speaker xc m isYƑwj Title OhJmjJl Abstract Ln̐lvŹA܂AÏkn̗_ɕsȃc[ƂȂĂ邪A@Ɉ˂炸̍sɑjނ̂ALTCYʂƋEʂłBX́AŇƂɁA̓̌̕ʂLIɏA\TCg̗Liqn̗ʎq̖ɂāAoN̕ʂ[I10^{-4}̐xœ͕@҂ݏoB̓Iɂ, [̊JÊƁAn̒ŃGlM[XP[őɂA[ŗƂ悤Ȋɂ₩ȃXP[OsBXP[O֐ɂ́A炪lĂsine^2֐[2]ϋɓIɗpAGlM[̒[Ԃ𐶐B̒[Ԃ LIɌn̒ƒfMIɐڑA[Ԃobt@ƂČn̒oNȏԂɕϕIɋ߂Â邱Ƃ\ɂȂB̕@_ɂA܂ŊKiłȂʎqXsn̎ߒAdqn̗q-w|eVȐ炩ȋȐƂāAxŌɍČ邱Ƃ炩ɂȂB{uł́AWilsoňJ荞݌Q̍lƂɁA̎@̃JjỶs, Qւ̉pƂēꂽ OpiqȂǂ̎ߒЉ[3]B[1] C. Hotta and N. Shibata, Phys. Rev. B 86, R041108 (2012).[2] A. Gendiar, R. Krcmar and T. Nishino, Prog. Theor. Phys. 122, 953 (2009); Prog. Theor. Phys. 123, 393 (2010).[3] C. Hotta, S. Nishimoto and N. Shibata, Phys. Rev. B. 87, 115128(2013).

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2012/12/10 (Mo) 15:00-16:30, room 829, Building 16, Komaba I campus, the University of Tokyo.

 Speaker  F iM1j Title d݂钷n̔M͊w\ Abstract @M͊w͊O̎dwǕKvƂɕ̕EłƂuv肵Ă邪AȆSĂ݂̐̕ł͂ȂBN[̌n̂悤ɗqԂ̑ݍp܂ŋyԁunv̑\łB̂悤Ȍnł̓Ggs[Ȃǂ̔M͊wɂēʐꎟƂُȐUƂmĂA]̔M͊ŵ܂ܓKp邱Ƃ͂łȂB@ŔM͊w̋AؔrAv͊w̉肷uďv݂̂F߂ƂɔM͊ŵǂ܂łAǂ炪j]݂̂B@ƁA񑊉IȌn̔M͊w̋c_ő݂悤 Tsallis Ggs[VIɓƂƂƂA]̓v͊wŗpĂ Gibbs Ggs[p邱Ƃŏ]ʂ̔M͊w\قڂ̂܂ܑ݂邱ƂB܂Ałɏqׂ悤ȔM͊ẅُȐUɑ΂ĂƕIȉ߂邱ƂłÁuvƂ͂ނÂ悤Ȍn̓FłƑ邱ƂB

2011/05/26 (Th) 14:40-16:10, room 410, Building 16, Komaba I campus, the University of Tokyo.

 Speaker Y iM2j Title T^IȏԂpv͊w̌vZ@ Abstract @ v͊wɂƁA~NJmjJWc̒Cӂ1ʎqԂIׂ΁Aʂɂꂪenergy eigenstatełȂĂA|IȊmŁA}Nʂ̐l^iAKvȂAdjB̌ϋɓIɗp }Nn̓v͊wI𐔒lvZV@ĂB@́iXsnjɂĂ̎@iMFSAhFO jB(E,N,M)Ŏw肳~NJmjJWci⑼̏WcjƓȏWcłA(E,N,h)Ŏw肳^~NJmjJWcl Bv͊wɂƁAqxgԂ̒́ȀWc̏ԒB镔Ԃ̒ACӂ1ʎqԂƂĂ΁A|IȊmŁA}N ʂ̐l^B̂悤ȁuT^Iȏԁv́Aenergy eigenstatełKv͂Ȃ̂ŁA_xNgɃn~gjȂ񂩂ZĂ䂭AƂɂ߂ĊȒPIȕ@ 邱ƂłB@̕@́Â悤ȗ_FPDŝZ邾Ȃ̂ŁA|IɑBQDA傫ȌnłvZ₷BRDLx̏ԂvZłBSD肪oȂ̂ŁAfrustration̂nɂgBTDT^IȔg֐܂̂ŁA֊֐ȂǂvZłB@ ̕@̗L𒲂ׂ邽߂ɁAmĂA1D Heisenberg model in a magnetic field ɓKpAƔrƂAM vs. h ̃OtAȆSĂ̒lɂāAɂ悭ƈvBRef. S. Sugiura and A. Shimizu, in preparation.

### Mini Workshop at Komaba: Quantum Transport and Manipulation, Oct. 7, 2010

2010/10/7 (Th) 13:45-17:30
Room 129, ground floor, building 16, Komaba I Campus, the University of Tokyo.

### New: Group photos are available : 1 2

#### Feedback Control of Quantum Transport

Monitoring quantum objects  during their time evolution usually introduces extra noise, but it can also compensate backaction effects and be used for recycling information in order to control the system dynamics.  This is also of interest for various NEMS applications.
In this talk, I will discuss electronic fluctuations which have become a major tool for probing quantum coherence, interactions, and dissipation effects in quantum transport through nanoscale structures. The random tunnelling of electrons in quantum transport is described by the full counting statistics (FCS) of transferred charges.  In analogy to equilibrium thermodynamics where, e.g., the cumulants of the particle number distribution in the grand canonical ensemble are proportional to the volume,  FCS cumulants in stationary transport linearly increase in time (exceptions are possible). All quantum transport devices thus have to deal with a stochastic element that can become a major obstacle when very regular currents are required.
Here, I show that this situation changes by  freezing' the cumulants in time, if one applies feedback (closed loop) control to  quantum transport. I propose a scheme where a time-dependent signal $q_n(t)$ is used to continuously adjust system parameters such as tunnel rates or energy levels.  Here, $q_n(t) \equiv I_{0}t -n$ is  an error charge determined from  the ideal target' current $I_{0}$ and the total charge $n$ that has been collected in  (or flown out of) a reservoir during the measurement (e.g., by a nearby quantum point contact detector) up to time $t$. The error charge determines whether to speed up or slow down the transport process -- a  form of feedback that is analogous to the centrifugal governor used, e.g., in thermo-mechanic machines like the steam engine. The  feedback scheme generates a new kind of FCS that can not be obtained via ordinary transport. This is analogous to feedback control in quantum optics, where an in-loop photocurrent was used in order to alter the photon statistics of a light beam.
(14:45-15:00 break)

#### Universal properties of response functions of nonequilibrium steady states

  Nonequilibrium statistical mechanics has been attracting much attention for long years. It was established in the linear nonequilibrium regime,' which is close to equilibrium. This regime can be described by the linear response theory,' which treats response of equilibrium states to weak external forces. The linear response theory yields many universal properties, which form a core of statistical mechanics in the linear nonequilibrium regime. In contrast, the nonlinear nonequilibrium regime,' which is not close to equilibrium, is only poorly understood.   In this talk, I generalize the linear response theory to the nonlinear nonequilibrium regime [1,2]. Specifically, I discuss linear response of nonequilibrium steady states (NESSs) far from equilibrium. Among the universal properties that existed in the linear nonequilibrium regime, some are lost in the nonlinear nonequilibrium regime.  However, the others survives if appropriately generalized.  I further generalize the theory to nonlinear response functions of NESSs [1,2]. Universal properties, which hold in diverse physical systems, are also found for 2nd and higher-order response functions of NESSs.   These universal properties of response functions of NESSs are illustrated for nonlinear optical materials and nonlinear electrical conductors. We have obtained remarkable results.  For example, the integral of differential conductivity over frequencies is independent of the degree of nonequilibrium. References: [1] A. Shimizu and T. Yuge, J. Phys. Soc. Jpn. 79 (2010) 013002. [2] A. Shimizu, to appear in J. Phys. Soc. Jpn.; arXiv:1007.4376.(16:00-16:30 break)

#### Deterministic photon-photon root-SWAP gate using a Lambda system

  We theoretically present a method to realize a deterministic photon-photon root-SWAP gate using a three-level Lambda system interacting with single photons in reflection geometry.  The Lambda system is used completely passively as a temporary memory for a photonic qubit; the initial state of the Lambda system may be arbitrary, and active control by auxiliary fields is unnecessary throughout the gate operations. These distinct merits make this entangling gate suitable for deterministic and scalable quantum computation.Reference:Phys. Rev. A 82, 010301(R) (2010)http://physics.aps.org/synopsis-for/10.1103/PhysRevA.82.010301


#### Measurement of bath spectrum by multiple pulse sequence in NMR

  In recent years there have been some reports of NMR experiments [1] that decoherence is suppressed by applying a sequence of radio-frequency pulses. This is qualitatively explained by the dynamical decoupling [2].  In this work we analyze the spin-boson model [3] with a pulse sequence to compare the theory and the experiment quantitatively. We find that the long-time behavior of the decay curve of the coherence provides the information of the boson bath spectrum. We propose a form of the bath spectrum to fit the experimental data and analyze the results for 75As in GaAs, 29Si in silicon and 23Na in NaCl.[1] S. Watanabe and S. Sasaki, Jpn. J. Appl. Phys. vol. 42 (2003) L1350.[2] L. Viola and S. Lloyd, Phys. Rev. A vol. 58 (1998) 2733.[3] A. J. Leggett et. al., Rev. Mod. Phys. vol. 59 (1987) 1.

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