edoc: No conditions. Results ordered -Date Deposited. 2024-08-08T22:47:35ZEPrintshttps://edoc.unibas.ch/images/uni-logo.jpghttps://edoc.unibas.ch/2021-05-11T09:42:33Z2021-05-11T09:44:42Zhttps://edoc.unibas.ch/id/eprint/82994This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829942021-05-11T09:42:33ZQuasi-probability distributions for observables in dynamic systemsWe develop a general framework to investigate fluctuations of non-commuting observables. To this end, we consider the Keldysh quasi-probability distribution (KQPD). This distribution provides a measurement-independent description of the observables of interest and their time-evolution. Nevertheless, positive probability distributions for measurement outcomes can be obtained from the KQPD by taking into account the effect of measurement back-action and imprecision. Negativity in the KQPD can be linked to an interference effect and acts as an indicator for non-classical behavior. Notable examples of the KQPD are the Wigner function and the full counting statistics, both of which have been used extensively to describe systems in the absence as well as in the presence of a measurement apparatus. Here we discuss the KQPD and its moments in detail and connect it to various time-dependent problems including weak values, fluctuating work, and Leggett-Garg inequalities. Our results are illustrated using the simple example of two subsequent, non-commuting spin measurements. Patrick P. Hofer2021-05-11T09:39:06Z2021-05-11T09:40:49Zhttps://edoc.unibas.ch/id/eprint/82979This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829792021-05-11T09:39:06ZFundamental limits on low-temperature quantum thermometry with finite resolutionWhile the ability to measure low temperatures accurately in quantum systems is important in a wide range of experiments, the possibilities and the fundamental limits of quantum thermometry are not yet fully understood theoretically. Here we develop a general approach to low-temperature quantum thermometry, taking into account restrictions arising not only from the sample but also from the measurement process. We derive a fundamental bound on the minimal uncertainty for any temperature measurement that has a finite resolution. A similar bound can be obtained from the third law of thermodynamics. Moreover, we identify a mechanism enabling sub-exponential scaling, even in the regime of finite resolution. We illustrate this effect in the case of thermometry on a fermionic tight-binding chain with access to only two lattice sites, where we find a quadratic divergence of the uncertainty. We also give illustrative examples of ideal quantum gases and a square-lattice Ising model, highlighting the role of phase transitions. Patrick P. PottsJonatan Bohr BraskNicolas Brunner2021-05-11T08:52:49Z2021-05-11T08:52:49Zhttps://edoc.unibas.ch/id/eprint/82998This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829982021-05-11T08:52:49ZMach-Zehnder interferometry with periodic voltage pulsesWe investigate theoretically a Mach-Zehnder interferometer driven by a time-dependent voltage. Motivated by recent experiments, we focus on a train of Lorentzian voltage pulses which we compare to a sinusoidal and a constant voltage. We discuss the visibilities of Aharonov-Bohm oscillations in the current and in the noise. For the current, we find a strikingly different behavior in the driven as compared to the static case for voltage pulses containing multiple charges. For pulses containing fractional charges, we find a universality at path-length differences equal to multiples of the spacing between the voltage pulses. These observations can be explained by the electronic energy distribution of the driven contact. In the noise oscillations, we find additional features which are characteristic to time-dependent transport. Finite electronic temperatures are found to have a qualitatively different influence on the current and the noise. Patrick P. HoferChristian Flindt2021-05-11T08:52:30Z2021-05-11T08:52:30Zhttps://edoc.unibas.ch/id/eprint/82989This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829892021-05-11T08:52:30ZNegative Full Counting Statistics Arise from Interference EffectsThe Keldysh-ordered full counting statistics is a quasiprobability distribution describing the fluctuations of a time-integrated quantum observable. While it is well known that this distribution can fail to be positive, the interpretation and origin of this negativity has been somewhat unclear. Here, we show how the full counting statistics can be tied to trajectories through Hilbert space, and how this directly connects negative quasiprobabilities to an unusual interference effect. Our findings are illustrated with the example of energy fluctuations in a driven bosonic resonator; we discuss how negative quasiprobability here could be detected experimentally using superconducting microwave circuits. Patrick P. HoferA. A. Clerk2021-05-11T08:50:33Z2021-05-26T07:16:24Zhttps://edoc.unibas.ch/id/eprint/82996This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829962021-05-11T08:50:33ZElectron waiting times in coherent conductors are correlatedWe evaluate the joint distributions of electron waiting times in coherent conductors described by scattering theory. Successive electron waiting times in a single-channel conductor are found to be correlated due to the fermionic statistics encoded in the many-body state. Our formalism allows us also to investigate the waiting times between charge transfer events in different outgoing channels. As an application we consider a quantum point contact in a chiral setup with one or both input channels biased by either a static or a time-dependent periodic voltage described by Floquet theory. The theoretical framework developed here can be applied to a variety of scattering problems and can in a straightforward manner be extended to joint distributions of several electron waiting times. David DasenbrookPatrick P. HoferChristian Flindt2021-05-11T08:42:00Z2021-05-11T08:42:00Zhttps://edoc.unibas.ch/id/eprint/82992This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829922021-05-11T08:42:00ZQuantum Thermal Machine as a ThermometerWe propose the use of a quantum thermal machine for low-temperature thermometry. A hot thermal reservoir coupled to the machine allows for simultaneously cooling the sample while determining its temperature without knowing the model-dependent coupling constants. In its most simple form, the proposed scheme works for all thermal machines that perform at Otto efficiency and can reach Carnot efficiency. We consider a circuit QED implementation that allows for precise thermometry down to ∼15 mK with realistic parameters. Based on the quantum Fisher information, this is close to the optimal achievable performance. This implementation demonstrates that our proposal is particularly promising in systems where thermalization between different components of an experimental setup cannot be guaranteed. Patrick P. HoferJonatan Bohr BraskMarti Perarnau-LlobetNicolas Brunner2021-05-11T08:27:22Z2021-05-26T07:17:53Zhttps://edoc.unibas.ch/id/eprint/82990This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829902021-05-11T08:27:22ZQuantum heat engines based on electronic Mach-Zehnder interferometersWe theoretically investigate the thermoelectric properties of heat engines based on Mach-Zehnder interferometers. The energy dependence of the transmission amplitudes in such setups arises from a difference in the interferometer arm lengths. Any thermoelectric response is thus of purely quantum-mechanical origin. In addition to an experimentally established three-terminal setup, we also consider a two-terminal geometry as well as a four-terminal setup consisting of two interferometers. We find that Mach-Zehnder interferometers can be used as powerful and efficient heat engines which perform well under realistic conditions. Patrick P. HoferBjoern Sothmann2021-05-11T08:24:01Z2021-05-26T07:15:55Zhttps://edoc.unibas.ch/id/eprint/82991This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829912021-05-11T08:24:01ZQuantum heat engine based on photon-assisted Cooper pair tunnelingWe propose and analyze a simple mesoscopic quantum heat engine that exhibits both high power and high efficiency. The system consists of a biased Josephson junction coupled to two microwave cavities, with each cavity coupled to a thermal bath. Resonant Cooper pair tunneling occurs with the exchange of photons between cavities, and a temperature difference between the baths can naturally lead to a current against the voltage, and hence work. As a consequence of the unique properties of Cooper-pair tunneling, the heat current is completely separated from the charge current. This combined with the strong energy selectivity of the process leads to an extremely high efficiency. Patrick P. HoferJ. -R. SouquetA. A. Clerk2021-05-11T08:23:57Z2021-05-11T08:28:15Zhttps://edoc.unibas.ch/id/eprint/82993This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829932021-05-11T08:23:57ZAutonomous quantum refrigerator in a circuit QED architecture based on a Josephson junctionAn implementation of a small quantum absorption refrigerator in a circuit QED architecture is proposed. The setup consists of three harmonic oscillators coupled to a Josephson junction. The refrigerator is autonomous in the sense that it does not require any external control for cooling, but only thermal contact between the oscillators and heat baths at different temperatures. In addition, the setup features a built-in switch, which allows the cooling to be turned on and off. If timing control is available, this enables the possibility for coherence-enhanced cooling. Finally, we show that significant cooling can be achieved with experimentally realistic parameters and that our setup should be within reach of current technology. Patrick P. HoferMarti Perarnau-LlobetJonatan Bohr BraskRalph SilvaMarcus HuberNicolas Brunner2021-05-11T08:15:37Z2021-05-11T08:31:10Zhttps://edoc.unibas.ch/id/eprint/82995This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829952021-05-11T08:15:37ZOn-demand entanglement generation using dynamic single-electron sourcesWe review our recent proposals for the on-demand generation of entangled few-electron states using dynamic single-electron sources. The generation of entanglement can be traced back to the single-electron entanglement produced by quantum point contacts (QPCs) acting as electronic beam splitters. The coherent partitioning of a single electron leads to entanglement between the two outgoing arms of the QPC. We describe our various approaches for generating and certifying entanglement in dynamic electronic conductors and we quantify the influence of detrimental effects such as finite electronic temperatures and other dephasing mechanisms. The prospects for future experiments are discussed and possible avenues for further developments are identified. [GRAPHICS] (a) The coherent partitioning of a single electron on a QPC leads to entanglement between the outgoing arms. The entanglement can be detected using two copies of the state. (b) A time-bin entangled state is generated by partitioning two electrons on a QPC followed by projection onto the subspace with one electron in each arm. The two-electron entanglement is due to the entanglement of the individual single-electron states. In both panels, circles represent single-electron sources and squares represent detectors. Patrick P. HoferDavid DasenbrookChristian Flindt2021-05-11T08:14:53Z2021-05-11T08:16:13Zhttps://edoc.unibas.ch/id/eprint/82997This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829972021-05-11T08:14:53ZElectron waiting times for the mesoscopic capacitorWe evaluate the distribution of waiting times between electrons emitted by a driven mesoscopic capacitor. Based on a wave packet approach we obtain analytic expressions for the electronic waiting time distribution and the joint distribution of subsequent waiting times. These semi-classical results are compared to a full quantum treatment based on Floquet scattering theory and good agreement is found in the appropriate parameter ranges. Our results provide an intuitive picture of the electronic emissions from the driven mesoscopic capacitor and may be tested in future experiments. Patrick P. HoferDavid DasenbrookChristian Flindt2021-05-11T08:14:08Z2021-05-26T07:15:19Zhttps://edoc.unibas.ch/id/eprint/82999This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829992021-05-11T08:14:08ZMarkovian master equations for quantum thermal machines: local versus global approachThe study of quantum thermal machines, and more generally of open quantum systems, often relies on master equations. Two approaches are mainly followed. On the one hand, there is the widely used, but often criticized, local approach, where machine sub-systems locally couple to thermal baths. On the other hand, in the more established global approach, thermal baths couple to global degrees of freedom of the machine. There has been debate as to which of these two conceptually different approaches should be used in situations out of thermal equilibrium. Here we compare the local and global approaches against an exact solution for a particular class of thermal machines. We consider thermodynamically relevant observables, such as heat currents, as well as the quantum state of the machine. Our results show that the use of a local master equation is generally well justified. In particular, for weak inter-system coupling, the local approach agrees with the exact solution, whereas the global approach fails for non-equilibrium situations. For intermediate coupling, the local and the global approach both agree with the exact solution and for strong coupling, the global approach is preferable. These results are backed by detailed derivations of the regimes of validity for the respective approaches. Patrick P. HoferMarti Perarnau-LlobetL. David M. MirandaGeraldine HaackRalph SilvaJonatan Bohr BraskNicolas Brunner2021-05-11T08:13:25Z2021-05-11T08:17:36Zhttps://edoc.unibas.ch/id/eprint/83000This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/830002021-05-11T08:13:25ZProposal for an ac spin current sourceWe propose an ac current source that can be tuned from a pure charge to a pure spin current source. The device consists of two mesoscopic capacitors attached to a two-dimensional strip of a topological insulator. The change from charge to spin current is controlled by an offset in the top gate potentials that drive the capacitors. In addition to this setup, which anticipates the experimental realisation of quantum point contacts in topological insulators, we propose an analogous source in the quantum Hall regime which only relies on presently available building blocks. To this end, we calculate the band structure of a topological insulator in a magnetic field. The intrinsic spin-orbit coupling, together with a split gate, allows for an analogous source, where charge and spin current can be manipulated. The realisation of the device as well as the detection of the ac spin current are within reach of the present experimental technology. Patrick P. HoferHugo AramberriChristoph SchenkePierre A. L. Delplace2021-05-10T15:49:38Z2021-05-10T15:49:38Zhttps://edoc.unibas.ch/id/eprint/82981This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829812021-05-10T15:49:38ZDetailed Fluctuation Relation for Arbitrary Measurement and Feedback SchemesFluctuation relations are powerful equalities that hold far from equilibrium. However, the standard approach to include measurement and feedback schemes may become inapplicable in certain situations, including continuous measurements, precise measurements of continuous variables, and feedback induced irreversibility. Here we overcome these shortcomings by providing a recipe for producing detailed fluctuation relations. Based on this recipe, we derive a fluctuation relation which holds for arbitrary measurement and feedback control. The key insight is that fluctuations inferable from the measurement outcomes may be suppressed by postselection. Our detailed fluctuation relation results in a stringent and experimentally accessible inequality on the extractable work, which is saturated when the full entropy production is inferable from the data. Patrick P. PottsPeter Samuelsson2021-05-10T15:49:23Z2021-05-26T07:14:49Zhttps://edoc.unibas.ch/id/eprint/82980This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829802021-05-10T15:49:23ZMaxwell's demon in a double quantum dot with continuous charge detectionConverting information into work has, during the past decade, gained renewed interest as it gives insight into the relation between information theory and thermodynamics. Here, we theoretically investigate an implementation of Maxwell's demon in a double quantum dot and demonstrate how heat can be converted into work using only information. This is accomplished by continuously monitoring the charge state of the quantum dots and transferring electrons against a voltage bias using a feedback scheme. We investigate the electrical work produced by the demon and find a non-Gaussian work distribution. To illustrate the effect of a realistic charge detection scheme, we develop a model taking into account noise as well as a finite delay time and show that an experimental realization is feasible with present day technology. Depending on the accuracy of the measurement, the system is operated as an implementation of Maxwell's demon or a single-electron pump. Bjorn Annby-AnderssonPeter SamuelssonVille F. MaisiPatrick P. Potts2021-05-10T15:39:32Z2021-05-10T15:39:32Zhttps://edoc.unibas.ch/id/eprint/82983This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829832021-05-10T15:39:32ZQuantum teleportation of single-electron statesWe consider a scheme for on-demand teleportation of a dual-rail electron qubit state, based on single-electron sources and detectors. The scheme has a maximal efficiency of 25%, which is limited both by the shared entangled state as well as the Bell-state measurement. We consider two experimental implementations, realizable with current technology. The first relies on surface acoustic waves, where all the ingredients are readily available. The second is based on Lorentzian voltage pulses in quantum Hall edge channels. As single-electron detection is not yet experimentally established in these systems, we consider a tomographic detection of teleportation using current correlators up to (and including) third order. For both implementations, we take into account environmental effects. Edvin OlofssonPeter SamuelssonNicolas BrunnerPatrick P. Potts2021-05-10T15:39:25Z2021-05-26T07:18:22Zhttps://edoc.unibas.ch/id/eprint/82987This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829872021-05-10T15:39:25ZEmission of time-bin entangled particles into helical edge statesWe propose a single-particle source which emits into the helical edge states of a two-dimensional quantum spin Hall insulator. Without breaking time-reversal symmetry, this source acts like a pair of noiseless single-electron emitters which each inject separately into a chiral edge state. By locally breaking time-reversal symmetry, the source becomes a proper single-particle emitter which exhibits shot noise. Due to its intrinsic helicity, this system can be used to produce time-bin entangled pairs of electrons in a controlled manner. The noise created by the source contains information on the emitted wave packets and is proportional to the concurrence of the emitted state. Patrick P. HoferMarkus Buettiker2021-05-10T15:38:58Z2021-05-10T15:38:58Zhttps://edoc.unibas.ch/id/eprint/82988This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829882021-05-10T15:38:58ZSingle-electron entanglement and nonlocalityMotivated by recent progress in electron quantum optics, we revisit the question of single-electron entanglement, specifically whether the state of a single electron in a superposition of two separate spatial modes should be considered entangled. We first discuss a gedanken experiment with single-electron sources and detectors, and demonstrate deterministic (i. e. without post-selection) Bell inequality violation. This implies that the single-electron state is indeed entangled and, furthermore, nonlocal. We then present an experimental scheme where single-electron entanglement can be observed via measurements of the average currents and zero-frequency current cross-correlators in an electronic Hanbury Brown–Twiss interferometer driven by Lorentzian voltage pulses. We show that single-electron entanglement is detectable under realistic operating conditions. Our work settles the question of single-electron entanglement and opens promising perspectives for future experiments. David DasenbrookJoseph BowlesJonatan Bohr BraskPatrick P. HoferChristian FlindtNicolas Brunner2021-05-10T15:32:40Z2021-05-10T15:32:40Zhttps://edoc.unibas.ch/id/eprint/82986This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829862021-05-10T15:32:40ZThermodynamic uncertainty relations including measurement and feedbackThermodynamic uncertainty relations quantify how the signal-to-noise ratio of a given observable is constrained by dissipation. Fluctuation relations generalize the second law of thermodynamics to stochastic processes. We show that any fluctuation relation directly implies a thermodynamic uncertainty relation, considerably increasing their range of applicability. In particular, we extend thermodynamic uncertainty relations to scenarios which include measurement and feedback. Since feedback generally breaks time-reversal invariance, the uncertainty relations involve quantities averaged over the forward and the backward experiment defined by the associated fluctuation relation. This implies that the signal-to-noise ratio of a given experiment can in principle become arbitrarily large as long as the corresponding backward experiment compensates, e.g., by being sufficiently noisy. We illustrate our results with the Szilard engine as well as work extraction by free energy reduction in a quantum dot. Patrick P. PottsPeter Samuelsson2021-05-10T15:31:32Z2021-05-10T15:31:32Zhttps://edoc.unibas.ch/id/eprint/82985This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829852021-05-10T15:31:32ZPower, Efficiency and Fluctuations in a Quantum Point Contact as Steady-State Thermoelectric Heat EngineThe trade-off between large power output, high efficiency and small fluctuations in the operation of heat engines has recently received interest in the context of thermodynamic uncertainty relations (TURs). Here we provide a concrete illustration of this trade-off by theoretically investigating the operation of a quantum point contact (QPC) with an energy-dependent transmission function as a steady-state thermoelectric heat engine. As a starting point, we review and extend previous analysis of the power production and efficiency. Thereafter the power fluctuations and the bound jointly imposed on the power, efficiency, and fluctuations by the TURs are analyzed as additional performance quantifiers. We allow for arbitrary smoothness of the transmission probability of the QPC, which exhibits a close to step-like dependence in energy, and consider both the linear and the non-linear regime of operation. It is found that for a broad range of parameters, the power production reaches nearly its theoretical maximum value, with efficiencies more than half of the Carnot efficiency and at the same time with rather small fluctuations. Moreover, we show that by demanding a non-zero power production, in the linear regime a stronger TUR can be formulated in terms of the thermoelectric figure of merit. Interestingly, this bound holds also in a wide parameter regime beyond linear response for our QPC device Sara KheradsoudNastaran DashtiMaciej MisiornyPatrick P. PottsJanine SplettstoesserPeter Samuelsson2021-05-10T15:28:56Z2021-05-10T15:28:56Zhttps://edoc.unibas.ch/id/eprint/82984This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829842021-05-10T15:28:56ZTight bound on finite-resolution quantum thermometry at low temperaturesMathias R. JorgensenPatrick P. PottsMatteo G. A. ParisJonatan B. Brask2021-05-10T15:27:11Z2021-05-10T15:27:11Zhttps://edoc.unibas.ch/id/eprint/82982This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829822021-05-10T15:27:11ZCertifying Nonclassical Behavior for Negative Keldysh QuasiprobabilitiesPatrick P. Potts2021-05-10T15:26:28Z2021-05-10T15:26:28Zhttps://edoc.unibas.ch/id/eprint/82978This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829782021-05-10T15:26:28ZAutonomous conversion of information to work in quantum dotsRafael SanchezPeter SamuelssonPatrick P. Potts2021-05-10T15:19:44Z2021-05-10T15:20:09Zhttps://edoc.unibas.ch/id/eprint/82977This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/829772021-05-10T15:19:44ZHybrid thermal machines: Generalized thermodynamic resources for multitaskingGonzalo ManzanoRafael SanchezRalph SilvaGeraldine HaackJonatan B. BraskNicolas BrunnerPatrick P. Potts2019-02-06T14:53:32Z2021-05-08T03:10:49Zhttps://edoc.unibas.ch/id/eprint/68074This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/680742019-02-06T14:53:32ZOptimal work extraction from quantum states by photo-assisted Cooper pair tunnelingThe theory of quantum thermodynamics predicts fundamental bounds on work extraction from quantum states. As these bounds are derived in a very general and abstract setting, it is unclear how relevant they are in an experimental context, where control is typically limited. Here we address this question by showing that optimal work extraction is possible for a realistic engine. The latter consists of a superconducting circuit, where a LC-resonator is coupled to a Josephson junction. The oscillator state fuels the engine, providing energy absorbed by Cooper pairs, thus producing work in the form of an electrical current against an external voltage bias. We show that this machine can extract the maximal amount of work from all Gaussian and Fock states. Furthermore, we consider work extraction from a continuously stabilized oscillator state. In both scenarios, coherence between energy eigenstates is beneficial, increasing the power output of the machine. This is possible because the phase difference across the Josephson junction provides a phase reference. Niels LörchChristoph BruderNicolas BrunnerPatrick P. Hofer2013-03-01T11:07:29Z2021-05-26T07:19:46Zhttps://edoc.unibas.ch/id/eprint/24576This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/245762013-03-01T11:07:29ZSuperfluid drag of two-species Bose-Einstein condensates in optical latticesWe study two-species Bose-Einstein condensates in quasi-two-dimensional optical lattices of varying geometry and potential depth. Based on the numerically exact Bloch and Wannier functions obtained using the plane-wave expansion method, we quantify the drag (entrainment coupling) between the condensate components. This drag originates from the (short-range) interspecies interaction and increases with the kinetic energy. As a result of the interplay between interaction and kinetic energy effects, the superfluid-drag coefficient shows a nonmonotonic dependence on the lattice depth. To make contact with future experiments, we quantitatively investigate the drag for mass ratios corresponding to relevant atomic species. Patrick P. HoferC. BruderVladimir M. Stojanovic