We provide the first experimental confirmation of a three-way quantum coherence identity possessed by single pure-state photons. Our experimental results demonstrate that traditional wave-particle duality is specifically limited by this identity. As a consequence, we show that quantum duality itself can be amplified, attenuated, or turned completely off. In the Young double-slit context this quantum coherence identity is found to be directly relevant, and it supplies a rare quantitative backup for one of Bohr's philosophical pronouncements.
Fluctuation theorems are relations constraining the out-of-equilibrium fluctuations of thermodynamic quantities like the entropy production that were initially introduced for classical or quantum systems in contact with a thermal bath. Here we show, in the absence of thermal bath, the dynamics of continuously measured quantum systems can also be described by a fluctuation theorem, expressed in terms of a recently introduced arrow of time measure. This theorem captures the emergence of irreversible behavior from microscopic reversibility in continuous quantum measurements. From this relation, we demonstrate that measurement-induced wave-function collapse exhibits absolute irreversibility, such that Jarzynski and Crooks-like equalities are violated. We apply our results to different continuous measurement schemes on a qubit: dispersive measurement, homodyne and heterodyne detection of a qubit's fluorescence.The emergence of macroscopic irreversibility from microscopic time-reversal invariant physical laws has been a long-standing issue, well described by the formalism of statistical thermodynamics [1,2]. In this framework, the small system under study follows stochastic trajectories in its phase-space, where the randomness models the uncontrolled forces exerted on the system by its thermal environment. Although these trajectories are microscopically reversible, one direction of time is more probable than the other and a arrow of time emerges for the ensemble of trajectories. In this framework, the thermodynamic variables like the work, the heat and the entropy produced during a process appear as random variables, defined for a single realization (i.e. a single trajectory), whose averages comply with the first and second law of thermodynamics. Furthermore, the fluctuations of these quantities are constrained beyond the second law, as captured by the so-called Fluctuation Theorems (FT) [3][4][5], which can be written under the form e −σ(Γ) = 1, where σ(Γ) is the entropy production along a single trajectory Γ. We denote · , the ensemble average over the realizations of the studied process (or equivalently, over the possible trajectories). The entropy production σ(Γ) fulfilling the FT is equal to the ratio of the probability of the (forward in time) trajectory Γ and the probability of the time-reversed (or backward in time) trajectory corresponding to Γ. During the last decades, these results have been investigated in the quantum regime where the system and the thermal bath can be quantum systems, allowing the proof of quantum extensions of the FTs [6][7][8][9][10][11][12][13][14][15][16][17][18]. Experiments have demonstrated the validity of these FTs in both classical and quantum regimes [19][20][21][22][23][24].However, it was shown that the form of the FTs must be modified for special processes [25][26][27][28][29][30][31][32][33][34], which are such that some theoretically allowed backward trajectories do not have a forward-in-time counterpart. A canonical example is the free expansion of a single particle gas ini...
We establish an analogy between superconductor-metal interfaces and the quantum physics of a black hole, using the proximity effect. We show that the metal-superconductor interface can be thought of as an event horizon and Andreev reflection from the interface is analogous to the Hawking radiation in black holes. We describe quantum information transfer in Andreev reflection with a final state projection model similar to the Horowitz-Maldacena model for black hole evaporation. We also propose the Andreev reflection-analogue of Hayden and Preskill's description of a black hole final state, where the black hole is described as an information mirror. The analogy between Crossed Andreev Reflections and Einstein-Rosen bridges is discussed: our proposal gives a precise mechanism for the apparent loss of quantum information in a black hole by the process of nonlocal Andreev reflection, transferring the quantum information through a wormhole and into another universe. Given these established connections, we conjecture that the final quantum state of a black hole is exactly the same as the ground state wavefunction of the superconductor/superfluid in the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity; in particular, the infalling matter and the infalling Hawking quanta, described in the Horowitz-Maldacena model, forms a Cooper pair-like singlet state inside the black hole. A black hole evaporating and shrinking in size can be thought of as the analogue of Andreev reflection by a hole where the superconductor loses a Cooper pair. Our model does not suffer from the black hole information problem since Andreev reflection is unitary. We also relate the thermodynamic properties of a black hole to that of a superconductor, and propose an experiment which can demonstrate the negative specific heat feature of black holes in a growing/evaporating condensate.Comment: 19 pages, 7 figure
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.
Ac ombined theoretical and experimental investigation into the role of concerted long-(dipolec oupling) and short-range (orbitalo verlap mediated excimer) electronic interactions in modulating the emission of six crystalline acetylanthracenes( 1-3)i sr eported. Friedel-Crafts acylation of anthracene rendered crystalline acetylanthracenes with discrete close packing, varied orbitalo verlap, and resultant distinct emission (blue-green-yellow) from cooperative excimera nd dipole coupling. Time-resolved emission spectroscopy (TRES) studies and the Kasha's exciton theory based quantitative estimationo fd ipole coupling (mean-field approximation) substantiates the exciton dynamics in crystalline 1-3.E xtension of the Kasha'se xciton model beyond the traditional nearestneighbora pproach, and consistent agreement among the computed spectral shifts and TRES temporal components, corroborate ah olistic approach to decipher the exciton relaxationd ynamics in the molecular assembly of novel photonic materials. [a] A. M. Philip, Dr.M.H ariharan SchoolofC hemistry,Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
We expand the time reversal symmetry arguments of quantum mechanics, originally proposed by Wigner in the context of unitary dynamics, to contain situations including generalized measurements for monitored quantum systems. We propose a scheme to derive the time reversed measurement operators by considering the Schrödinger picture dynamics of a qubit coupled to a measuring device, and show that the time reversed measurement operators form a Positive Operator Valued Measure (POVM) set. We present three particular examples to illustrate time reversal of measurement operators : (1) the Gaussian spin measurement, (2) a dichotomous POVM for spin, and (3) the measurement of qubit fluorescence. We then propose a general rule to unravel any rank two qubit measurement, and show that the backward dynamics obeys the retrodicted equations of the forward dynamics starting from the time reversed final state. We demonstrate the time reversal invariance of dynamical equations using the example of qubit fluorescence. We also generalize the discussion of a statistical arrow of time for continuous quantum measurements introduced by Dressel et al. [Phys. Rev. Lett. 119, 220507 (2017)]: we show that the backward probabilities can be computed from a process similar to retrodiction from the time reversed final state, and extend the definition of an arrow of time to ensembles prepared with pre-and post-selections, where we obtain a non-vanishing arrow of time in general. We discuss sufficient conditions for when time's arrow vanishes and show our method also captures the contributions to time's arrow due to natural physical processes like relaxation of an atom to its ground state. As a special case, we recover the time reversibility of the weak value as its complex conjugate using our method, and discuss how our conclusions differ from the time-symmetry argument of Aharonov-Bergmann-Lebowitz (ABL) rule. I. INTRODUCTIONAlthough most 1 of the microscopic laws of physics are invariant under a suitable time reversal symmetry operation, there seems to exist a preferred ordering in which events are more likely to happen than otherwise, in the macroscopic world. This is true for a box of an ideal gas -where one can practically keep track of the dynamics of every single molecule given their initial conditions, and knowing all the microscopic interactions, while the second law of thermodynamics dictates that the gas molecules within the box re-distribute themselves and evolve towards a final state where the entropy is a maximum [4] -and in cosmology, from the observation of an expanding universe [5]. These apparent asymmetrical notions of time are also manifest in our everyday experiences as conscious observers; According to Wheeler, our notion of a past corresponds to experiencing a definite, informative, thus recordable set of events [6,7], and from an information theory perspective, they correspond to processes where entropy always increases or remains constant [7]. Understanding how a definite arrow of time emerges from a time reversal invar...
The origin of macroscopic irreversibility from microscopically time-reversible dynamical laws—often called the arrow-of-time problem—is of fundamental interest in both science and philosophy. Experimentally probing such questions in quantum theory requires systems with near-perfect isolation from the environment and long coherence times. Ultracold atoms are uniquely suited to this task. We experimentally demonstrate a striking parallel between the statistical irreversibility of wavefunction collapse and the arrow of time problem in the weak measurement of the quantum spin of an atomic cloud. Our experiments include statistically rare events where the arrow of time is inferred backward; nevertheless we provide evidence for absolute irreversibility and a strictly positive average arrow of time for the measurement process, captured by a fluctuation theorem. We further demonstrate absolute irreversibility for measurements performed on a quantum many-body entangled wavefunction—a unique opportunity afforded by our platform—with implications for studying quantum many-body dynamics and quantum thermodynamics.
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