Abstract
Time-domain interferometry (TDI) is a method to probe space-time correlations among particles in condensed matter systems. Applying TDI to quantum systems raises the general question, whether two-time correlations can be reliably measured without adverse impact of the measurement backaction onto the dynamics of the system. Here, we show that a recently developed quantum version of TDI (QTDI) indeed can access the full quantum-mechanical two-time correlations without backaction. We further generalize QTDI to weak classical continuous-mode coherent input states, alleviating the need for single-photon input fields. Finally, we interpret our results by splitting the space-time correlations into two parts. While the first one is associated to projective measurements and thus insensitive to backaction, we identify the second contribution as arising from the coherence properties of the state of the probed target system, such that it is perturbed or even destroyed by measurements on the system.
Highlights
Time-domain interferometry (TDI) is an experimental technique to probe space-time correlations among particles in condensed matter systems [1,2,3,4,5,6,7,8,9,10,11,12,13]
We apply the previous general discussion to the specific case of interest in the present work, and we show how the splitting into a projective and a coherent part applies to the dynamical couple correlation function (DCF), and how this modifies the features of the intermediate scattering function (ISF), for a quantum system composed of N particles
As discussed in the Introduction, the measurement of two-time correlations between two generic observables of a quantum system in general cannot be accomplished by probing the observables of interest at two consecutive times, because the first probing would backact on the system altering its successive dynamics and the results of the second probing
Summary
Time-domain interferometry (TDI) is an experimental technique to probe space-time correlations among particles in condensed matter systems [1,2,3,4,5,6,7,8,9,10,11,12,13]. It is known that the dynamics of a quantum system can be profoundly altered by the interaction with measurement devices [29] Because of this fact, in general quantummechanical time correlations between two observables cannot be obtained by probing the observables consecutively, as illustrated in Fig. 1(b) for a scattering setting as in TDI. In a purely classical picture of TDI, one might conclude that this technique is not suitable for probing space-time correlations of particles in quantum systems because it is based on two consecutive interventions on the system [the scattering of the two radiation pulses; see Fig. 1(b)]. In each repetition of the experiment, the system’s dynamics is not modified by the probing field before the single interaction takes place As a result, it was shown in [8] that QTDI provides access to the unperturbed ISF of the quantum system. We discuss how to measure the full quantum-mechanical ISF and DCF using QTDI, evading the measurement backaction
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