arXiv subjects

Andrew N. Jordan

Publications and source records attributed to Andrew N. Jordan.

At least 91 records · Page 5Linked to original sources

arXiv2020

Autonomous quantum absorption refrigerators

We propose a quantum absorption refrigerator using the quantum physics of resonant tunneling through quantum dots. The cold and hot reservoirs are fermionic leads, tunnel coupled via quantum dots to a central fermionic cavity, and we propose configurations in which the heat absorbed from the (very hot) central cavity is used as a resource to selectively transfer heat from the cold reservoir on the left, to the hot reservoir on the right. The heat transport in the device is particle---hole symmetric; we find two regimes of cooling as a function of the energy of the dots---symmetric with respect to the Fermi energy of the reservoirs---and we associate them to heat transfer by electrons above the Fermi level, and holes below the Fermi level, respectively. We also discuss optimizing the cooling effect by fine-tuning the energy of the dots as well as their linewidth, and characterize regimes where the transport is thermodynamically reversible such that Carnot Coefficent of Performance is achieved with zero cooling power delivered.

cond-mat.mes-hall↗

arXiv2020

An Interaction-Free Quantum Measurement-Driven Engine

Recently highly-efficient quantum engines were devised by exploiting the stochastic energy changes induced by quantum measurement. Here we show that such an engine can be based on an interaction-free measurement, in which the meter seemingly does not interact with the measured object. We use a modified version of the Elitzur-Vaidman bomb tester, an interferometric setup able to detect the presence of a bomb triggered by a single photon without exploding it. In our case, a quantum bomb subject to a gravitational force is initially in a superposition of being inside and outside one of the interferometer arms. We show that the bomb can be lifted without blowing up. This occurs when a photon traversing the interferometer is detected at a port that is always dark when the bomb is located outside the arm. The required potential energy is provided by the photon (which plays the role of the meter) even though it was not absorbed by the bomb. A natural interpretation is that the photon traveled through the arm which does not contain the bomb -- otherwise the bomb would have exploded -- but it implies the surprising conclusion that the energy exchange occurred at a distance despite a local interaction Hamiltonian. We use the weak value formalism to support this interpretation and find evidence of contextuality. Regardless of interpretation, this interaction-free quantum measurement engine is able to lift the most sensitive bomb without setting it off.

quant-ph↗

arXiv2020

Nonequilibrium Steady State and Heat Transport in Nonlinear Open Quantum Systems: Stochastic Influence Action and Functional Perturbative Analysis

In this paper, we show that a nonequilibrium steady state (NESS) exists at late times in open quantum systems with weak nonlinearity by following its nonequilibrium dynamics with a perturbative analysis. Here we consider an oscillator chain containing three-types of anharmonicity in the Fermi-Pasta-Ulam-Tsingou (FPUT) model: cubic $α$- and quartic $β$-type nearest-oscillator interactions and the on-site (pinned) Klein-Gordon (KG) quartic self-interaction. Assuming weak nonlinearity, we introduce a stochastic influence action approach to the problem and obtain the energy flow in different junctures of the chain. The formal results obtained here can be used for quantum transport problems in weakly nonlinear quantum systems. For $α$-type anharmonicity, we observe that the first-order corrections do not play any role in the thermal transport in the NESS of the configuration we considered. For KG and $β$-types anharmonicity, we work out explicitly the case of two weakly nonlinearly coupled oscillators, with results scalable to any number of oscillators. We examine the late-time energy flows from one thermal bath to the other via the coupled oscillators, and show that both the zeroth- and the first-order contributions of the energy flow become constant in time at late times, signaling the existence of a late-time NESS to first order in nonlinearity. Our perturbative calculations provide a measure of the strength of nonlinearity for nonlinear open quantum systems, which may help control the mesoscopic heat transport distinct from or close to linear transport. Furthermore, our results also give a benchmark for the numerical challenge of simulating heat transport. Our setup and predictions can be implemented and verified by investigating heat flow in an array of Josephson junctions in the limit of large Josephson energy with the platform of circuit QED.

quant-ph↗

arXiv2020

Black holes as Andreev reflecting mirrors

We propose a microscopic quantum description for Hawking radiation as Andreev reflections, which resolves the quantum information paradox at black hole event horizons. The detailed microscopic analysis presented here reveals how a black hole, treated as an Andreev reflecting mirror, provides a manifestly unitary description of an evaporating black hole, expanding our previous analysis presented in [PRD 96, 124011 (2017), PRD 98, 124043 (2018)]; In our analogy, a black hole resolves the information paradox by accepting particles -- pairing them with the infalling Hawking quanta into a Bardeen-Cooper-Schrieffer (BCS) like quantum ground state -- while Andreev reflecting the quantum information as encoded in outgoing Hawking radiation. The present approach goes beyond the black hole final state proposal by Horowitz and Maldacena [JHEP 02, 008 (2004)], by providing necessary microscopic details which allows us to circumvent important shortcomings of the black hole final state proposal. We also generalize the present Hamiltonian description to make an analogy to the apparent loss of quantum information possible in an Einstein-Rosen bridge, via crossed Andreev reflections.

gr-qc↗

arXiv2020

Quantifying the quantum heat contribution from a driven superconducting circuit

Unveiling the impact in thermodynamics of the phenomena specific to quantum mechanics is a crucial step to identify fundamental costs for quantum operations and quantum advantages in heat engines. We propose a two-reservoir setup to detect the quantum component in the heat flow exchanged by a coherently driven atom with its thermal environment. Tuning the driving parameters switches on and off the quantum and classical contributions to the heat flows, enabling their independent characterization. We demonstrate the feasibility of the measurement in a circuit-QED setup. Our results pave the road towards the first experimental verification of this quantum thermodynamic signature ubiquitous in quantum technologies.

quant-ph↗

arXiv2020

A two-qubit engine fueled by entangling operations and local measurements

We introduce a two-qubit engine that is powered by entangling operations and projective local quantum measurements. Energy is extracted from the detuned qubits coherently exchanging a single excitation. This engine, which uses the information and back-action of the measurement, is generalized to an N-qubit chain. We show that by gradually increasing the energy splitting along the chain, the initial low energy of the first qubit can be up-converted deterministically to an arbitrarily high energy at the last qubit by successive neighbor swap operations and local measurements. Modeling the local measurement as the entanglement of a qubit with a meter, we identify the measurement fuel as the energetic cost to erase correlations between the qubits.

quant-ph↗

arXiv2020

Conditional Teleportation of Quantum-Dot Spin States

Among the different platforms for quantum information processing, individual electron spins in semiconductor quantum dots stand out for their long coherence times and potential for scalable fabrication. The past years have witnessed substantial progress in the capabilities of spin qubits. However, coupling between distant electron spins, which is required for quantum error correction, presents a challenge, and this goal remains the focus of intense research. Quantum teleportation is a canonical method to transmit qubit states, but it has not been implemented in quantum-dot spin qubits. Here, we present evidence for quantum teleportation of electron spin qubits in semiconductor quantum dots. Although we have not performed quantum state tomography to definitively assess the teleportation fidelity, our data are consistent with conditional teleportation of spin eigenstates, entanglement swapping, and gate teleportation. Such evidence for all-matter spin-state teleportation underscores the capabilities of exchange-coupled spin qubits for quantum-information transfer.

cond-mat.mes-hall↗

arXiv2020

Measuring Fluorescence to Track a Quantum Emitter's State: A Theory Review

We review the continuous monitoring of a qubit through its spontaneous emission, at an introductory level. Contemporary experiments have been able to collect the fluorescence of an artificial atom in a cavity and transmission line, and then make measurements of that emission to obtain diffusive quantum trajectories in the qubit's state. We give a straightforward theoretical overview of such scenarios, using a framework based on Kraus operators derived from a Bayesian update concept; we apply this flexible framework across common types of measurements including photodetection, homodyne, and heterodyne monitoring, and illustrate its equivalence to the stochastic master equation formalism throughout. Special emphasis is given to homodyne (phase-sensitive) monitoring of fluorescence. The examples we develop are used to illustrate basic methods in quantum trajectories, but also to introduce some more advanced topics of contemporary interest, including the arrow of time in quantum measurement, and trajectories following optimal measurement records derived from a variational principle. The derivations we perform lead directly from the development of a simple model to an understanding of recent experimental results.

quant-ph↗

arXiv2020

Diffusive entanglement generation by continuous homodyne monitoring of spontaneous emission

We consider protocols to generate quantum entanglement between two remote qubits, through joint time-continuous detection of their spontaneous emission. We demonstrate that schemes based on homodyne detection, leading to diffusive quantum trajectories, lead to identical average entanglement yield as comparable photodetection strategies; this is despite substantial differences in the two-qubit state dynamics between these schemes, which we explore in detail. The ability to use different measurements to achieve the same ends may be of practical significance; the less-well-known diffusive scheme appears far more feasible on superconducting qubit platforms in the near term.

quant-ph↗

arXiv2019

Energy-Based Weak Measurement

When a well-localized photon is incident on a spatially superposed absorber but is not absorbed, the photon can still deliver energy to the absorber. It is shown that when the transferred energy is small relative to the energy uncertainty of the photon, this constitutes an unusual type of weak measurement of the absorber's energy, where the energy distribution of the unabsorbed photon acts as the measurement device, and the strongly disturbed state of the absorber becomes the effective pre-selection. Treating the final state of the absorber as the post-selection, it is shown that the absorber's energy increase is the weak value of its translational Hamiltonian, and the energy distribution of the photon shifts by the opposite amount. The basic case of non-scattering is examined, followed by the case of interaction-free energy transfer. Details and interpretations of the results are discussed.

quant-ph↗

arXiv2019

Quantum measurement engines and their relevance for quantum interpretations

This article presents recent progress in the theory of quantum measurement engines and discusses the implications of them for quantum interpretations and philosophical implications of the theory. Several new measurement engine designs are introduced and analyzed: We discuss a feedback based atom-and-piston engine that sharply associates all work with successful events and all quantum heat with the failed events, as well as an unconditional but coherent qubit engine that can attain perfect efficiency. Any quantum measurement of an observable that does not commute with the Hamiltonian will necessarily change the energy of the system. We discuss different ways to extract that energy, the efficiency and work production of that process.

quant-ph↗

arXiv2019

Optimal measurements for quantum multiparameter estimation with general states

We generalize the approach by Braunstein and Caves [Phys. Rev. Lett. 72, 3439 (1994)] to quantum multi-parameter estimation with general states. We derive a matrix bound of the classical Fisher information matrix due to each measurement operator. The saturation of all these bounds results in the saturation of the matrix Helstrom Cramér-Rao bound. Remarkably, the saturation of the matrix bound is equivalent to the saturation of the scalar bound with respect to any given positive definite weight matrix. Necessary and sufficient conditions are obtained for the optimal measurements that give rise to the Helstrom Cramér-Rao bound associated with a general quantum state. To saturate the Helstrom bound with separable measurements or collective measurement entangling only a small number of identical states, we find it is necessary for the symmetric logarithmic derivatives to commute on the support of the state. As an important application of our results, we construct several local optimal measurements for the problem of estimating the three-dimensional separation of two incoherent optical point sources.

quant-ph↗

arXiv2019

Diffraction-Based Interaction-Free Measurements

We introduce diffraction-based interaction-free measurements. In contrast with previous work where a set of discrete paths is engaged, good quality interaction-free measurements can be realized with a continuous set of paths, as is typical of optical propagation. If a bomb is present in a given spatial region -- so sensitive that a single photon will set it off -- its presence can still be detected without exploding it. This is possible because, by not absorbing the photon, the bomb causes the single photon to diffract around it. The resulting diffraction pattern can then be statistically distinguished from the bomb-free case. We work out the case of single- versus double- slit in detail, where the double-slit arises because of a bomb excluding the middle region.

quant-ph↗

arXiv2019

Superconducting quantum refrigerator: Breaking and rejoining Cooper pairs with magnetic field cycles

We propose a solid state refrigeration technique based on repeated adiabatic magnetization/demagnetization cycles of a superconductor which acts as the working substance. The gradual cooling down of a substrate (normal metal) in contact with the working substance is demonstrated for different initial temperatures of the substrate. Excess heat is given to a hot large-gap superconductor. The on-chip refrigerator works in a cyclic manner because of an effective thermal switching mechanism: Heat transport between N/N versus N/S junctions is asymmetric because of the appearance of the energy gap. This switch permits selective cooling of the metal. We find that this refrigeration technique can cool down a 0.3cm$^{3}$ block of Cu by almost two orders of magnitude starting from 200mK, and down to about 1mK starting from the base temperature of a dilution fridge (10mK). The corresponding cooling power for a 1cm$\times$1cm interface are 25 nW and 0.06 nW respectively, which scales with the area of the interface.

cond-mat.supr-con↗

arXiv2019

Quantum-limited estimation of the axial separation of two incoherent point sources

Improving axial resolution is crucial for three-dimensional optical imaging systems. Here we present a scheme of axial superresolution for two incoherent point sources based on spatial mode demultiplexing. A radial mode sorter is used to losslessly decompose the optical fields into a radial mode basis set to extract the phase information associated with the axial positions of the point sources. We show theoretically and experimentally that, in the limit of a zero axial separation, our scheme allows for reaching the quantum Cramér-Rao lower bound and thus can be considered as one of the optimal measurement methods. Unlike other superresolution schemes, this scheme does not require neither activation of fluorophores nor sophisticated stabilization control. Moreover, it is applicable to the localization of a single point source in the axial direction. Our demonstration can be useful to a variety of applications such as far-field fluorescence microscopy.

physics.optics↗

arXiv2019

Thermal transistor and thermometer based on Coulomb-coupled conductors

We study a three-terminal setup consisting of a single-level quantum dot capacitively coupled to a quantum point contact. The point contact connects to a source and drain reservoirs while the quantum dot is coupled to a single base reservoir. This setup has been used to implement a noninvasive, nanoscale thermometer for the bath reservoir by detecting the current in the quantum point contact. Here, we demonstrate that the device can also be operated as a thermal transistor where the average (charge and heat) current through the quantum point contact is controlled via the temperature of the base reservoir. We characterize the performances of this device both as a transistor and a thermometer, and derive the operating condition maximizing their respective sensitivities. The present analysis is useful for the control of charge and heat flow and high precision thermometry at the nanoscale.

cond-mat.mes-hall↗

arXiv2018

Gravitational sensing with weak value based optical sensors

Using weak values amplification angular resolution limits, we theoretically investigate the gravitational sensing of objects. By inserting a force-sensing pendulum into a weak values interferometer, the optical response can sense accelerations to a few 10's of $\mathrm{zepto}\text{-}\mathrm{g}/\sqrt{\mathrm{Hz}}$, with optical powers of $1~\mathrm{mW}$. We convert this precision into range and mass sensitivity, focusing in detail on simple and torsion pendula. Various noise sources present are discussed, as well as the necessary cooling that should be applied to reach the desired levels of precision.

physics.ins-det↗

arXiv2018

Bosons falling into a black hole: A superfluid analogue

We propose an analogy between the quantum physics of a black hole in its late stages of the evaporation process and a superfluid Bose Einstein Condensate (BEC), based on the Horowitz and Maldacena quantum final state projection model [JHEP 2004(02), 008]. The superfluid region is considered to be analogous to the interior of a black hole, and the normal fluid/superfluid interface is compared to the event horizon of a black hole. We theoretically investigate the possibility of recovering the wavefunction of particles incident on a superfluid BEC from the normal fluid, facilitated by the mode conversion processes occurring at the normal fluid/superfluid BEC interface. We also study how the correlations of an infalling mode with an external memory system can be preserved in the process, similar to Hayden and Preskill's "information mirror" model for a black hole [JHEP 2007(09), 120]. Based on these analogies, we conjecture that the quantum state of bosons entering a black hole in its final state is the superfluid quantum ground state of interacting bosons. Our analogy suggests that the wavefunction of bosons falling into a black hole can be recovered from the outgoing Hawking modes. In the particular case when a hole-like quasiparticle (a density dip) is incident on the superfluid BEC causing the superfluid to shrink in size, our model indicates that the evaporation is unitary.

gr-qc↗