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arXiv:2002.05883 · Quantum

Effect of environment on the interferometry of clocks

Harshit Verma, Magdalena Zych, Fabio Costa

Published Aug 17, 2021• 3 citations
arXivHTMLPDF

Abstract

Quantum interference of "clocks", namely of particles with time-evolving internal degrees of freedom (DOFs), is a promising avenue to test genuine general relativistic effects in quantum systems. The clock acquires which path information while experiencing different proper times on traversing the arms of the interferometer, leading to a drop in its path visibility. We consider scenarios where the clock is subject to environmental noise as it transits through the interferometer. In particular, we develop a generalized formulation of interferometric visibility affected by noise on the clock. We find that, for small noise and small proper time difference between the arms, the noise further reduces the visibility, while in more general situations it can either increase or reduce the visibility. As an example, we investigate the effect of a thermal environment constituted by a single field mode and show that the visibility drops further as the temperature is increased. Additionally, by considering noise models based on standard quantum channels, we show that interferometric visibility can increase or decrease depending on the type of noise and also the time scale and transition probabilities. The quantification of the effect of noise on the visibility – particularly in the case of a thermal environment paves the way for a better estimate on the expected outcome in an actual experiment.

DOI
10.22331/q-2021-08-17-525

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Quantum interference of "clocks", namely of particles with time-evolving internal degrees of freedom (DOFs), is a promising avenue to test genuine general relativistic effects in quantum systems. The clock acquires which path information while experiencing different proper times on traversing the arms of the interferometer, leading to a drop in its path visibility. We consider scenarios where the clock is subject to environmental noise as it transits through the interferometer. In particular, we develop a generalized formulation of interferometric visibility affected by noise on the clock. We find that, for small noise and small proper time difference between the arms, the noise further reduces the visibility, while in more general situations it can either increase or reduce the visibility. As an example, we investigate the effect of a thermal environment constituted by a single field mode and show that the visibility drops further as the temperature is increased. Additionally, by considering noise models based on standard quantum channels, we show that interferometric visibility can increase or decrease depending on the type of noise and also the time scale and transition probabilities. The quantification of the effect of noise on the visibility – particularly in the case of a thermal environment paves the way for a better estimate on the expected outcome in an actual experiment.
Current attempts to probe general relativistic effects in quantum mechanics focus on precision measurements of phase shifts in matter–wave interferometry. Yet, phase shifts can always be explained as arising because of an Aharonov–Bohm effect, where a particle in a flat space–time is subject to an effective potential. Here we propose a quantum effect that cannot be explained without the general relativistic notion of proper time. We consider interference of a 'clock'—a particle with evolving internal degrees of freedom—that will not only display a phase shift, but also reduce the visibility of the interference pattern. According to general relativity, proper time flows at different rates in different regions of space–time. Therefore, because of quantum complementarity, the visibility will drop to the extent to which the path information becomes available from reading out the proper time from the 'clock'. Such a gravitationally induced decoherence would provide the first test of the genuine general relativistic notion of proper time in quantum mechanics. In the theory of general relativity time flows at different rates depending on the space–time geometry. Here, a drop in the visibility of a quantum 'clock' interference in a gravitational potential is predicted, which cannot be explained without the general relativistic notion of time.
Quantum mechanics and general relativity have been extensively and independently confirmed in many experiments. However, the interplay of the two theories has never been tested: all experiments that measured the influence of gravity on quantum systems are consistent with non-relativistic, Newtonian gravity. On the other hand, all tests of general relativity can be described within the framework of classical physics. Here we discuss a quantum interference experiment with single photons that can probe quantum mechanics in curved space-time. We consider a single photon traveling in superposition along two paths in an interferometer, with each arm experiencing a different gravitational time dilation. If the difference in the time dilations is comparable with the photon's coherence time, the visibility of the quantum interference is predicted to drop, while for shorter time dilations the effect of gravity will result only in a relative phase shift between the two arms. We discuss what aspects of the interplay between quantum mechanics and general relativity are probed in such experiments and analyze the experimental feasibility.
Abstract Clock interferometry probes general-relativistic proper-time differences through the entanglement between a particle's center-of-mass path and its internal degrees of freedom. Existing analyses treat the internal clock as either a closed system or study how environmental noise modifies the interferometric visibility. Here we address a distinct question: what fraction of the proper-time-induced visibility loss remains recoverable when the experimentalist is restricted to local unitary control of the internal clock? We model the clock as a two-level system undergoing amplitude damping with branch-dependent proper times in a Mach-Zehnder interferometer and derive the visibility both without and with a spin-echo refocusing pulse. In the closed-system limit (γ→0\gamma\to0γ→0), the echo restores full visibility; for γ>0\gamma>0γ>0, the no-jump survival probability imposes a strict upper bound on echo-recovered visibility that no internal-only unitary can exceed. We establish the conditions under which a proper-time-parametrized Gorini-Kossakowski-Sudarshan-Lindblad equation is valid by appealing to the local comoving frame and the equivalence principle, distinguishing comoving-bath and laboratory-bath parametrizations. Numerical simulations with QuTiP confirm all analytic results. We provide experimental parameter estimates for cold-atom and cavity-QED platforms, showing that the irrecoverable visibility deficit is within reach of near-future clock-interferometry experiments. The echo-recovery deficit constitutes an operational witness that separates irreversible environmental decoherence from the formally reversible path-clock entanglement of the Pikovski mechanism.
Abstract In (Zych et al 2011 Nat. Commun. 2 505), the authors predicted that the interferometric visibility is affected by a gravitational field in way that cannot be explained without the general relativistic notion of proper time. In this work, we take a different route and start deriving the same effect using the unitary representation of the local Lorentz transformation in the Newtonian limit. In addition, we show that the effect on the interferometric visibility due to gravity persists in different spacetime geometries. However, the influence is not necessarily due to the notion of proper time. For instance, by constructing a ‘astronomical’ Mach–Zehnder interferometer in the Schwarzschild spacetime, the influence on the interferometric visibility can be due to another general relativistic effect, the geodetic precession. Besides, by using the unitary representation of the local Lorentz transformation, we show that this behavior of the interferometric visibility is general for an arbitrary spacetime, provided that we restrict the motion of the quanton to a two-dimensional spacial plane.
This work derives a conservative, operational consequence of the Scalar Temporal Field Ontology (STFO), in which time is modeled as a physical scalar field τ(xμ)\tau(x^\mu)τ(xμ) whose timelike gradient defines a preferred notion of evolution. We show that any two-path interference experiment (optical or matter-wave) yields a quantitative bound on unresolved temporal path-difference fluctuations. Interferometric visibility is identified with the characteristic function of the temporal fluctuation δΔτ\delta\Delta\tauδΔτ, leading to a model-independent constraint on the root-mean-square temporal noise in terms of the measured visibility and the experiment’s phase-generating energy scale. The analysis is intentionally operational and conservative. It does not modify standard quantum probabilities and is compatible with conventional environmental decoherence, appearing as an additional multiplicative coherence factor. Null results therefore impose direct experimental bounds on temporal-field fluctuations within the STFO framework. This paper interfaces quantum foundations, interferometry, and the problem of time, and provides a falsifiable, experiment-facing bridge between the Scalar Temporal Field Ontology and precision laboratory tests.
The phase of matter waves depends on proper time and is therefore susceptible to special-relativistic (kinematic) and gravitational (redshift) time dilation. Hence, it is conceivable that atom interferometers measure general-relativistic time-dilation effects. In contrast to this intuition, we show that (i) closed light-pulse interferometers without clock transitions during the pulse sequence are not sensitive to gravitational time dilation in a linear potential. (ii) They can constitute a quantum version of the special-relativistic twin paradox. (iii) Our proposed experimental geometry for a quantum-clock interferometer isolates this effect.