Abstract:We consider quantum signaling between two-level quantum systems in a cavity in the perturbative regime of the earliest possible arrival times of the signal. We present two main results: First, we find that, perhaps surprisingly, the analog of amplitude modulated signaling (Alice using her energy eigenstates |g , |e , as in the Fermi problem) is generally suboptimal for communication, namely, e.g., phase-modulated signaling (Alice using, e.g., {|+ , |− } states) overcomes the quantum noise already at a lower or… Show more
“…This detector couples locally to a scalar quantum field according to the Unruh-DeWitt model [26], which succeeds in capturing most of the fundamental features of the light-matter interaction when angular momentum exchange does not play a dominant role in the detector's dynamics [13,27,28]. This simple but powerful detector model has been successfully used to analyze information flows in relativistic settings in previous literature [29][30][31][32][33][34]. The model considers the detector to be a two-level quantum system (i.e.…”
We analyze the interactions of particle detectors with coherent states of a free scalar field. We find that the eigenvalues of the post-interaction density matrices of i) a single detector, ii) two detectors, and iii) the partial transpose of the latter, are all independent of which coherent state the field was in. A consequence of these results is that a detector pair can harvest the same amount of entanglement from any coherent field state as from the vacuum.
“…This detector couples locally to a scalar quantum field according to the Unruh-DeWitt model [26], which succeeds in capturing most of the fundamental features of the light-matter interaction when angular momentum exchange does not play a dominant role in the detector's dynamics [13,27,28]. This simple but powerful detector model has been successfully used to analyze information flows in relativistic settings in previous literature [29][30][31][32][33][34]. The model considers the detector to be a two-level quantum system (i.e.…”
We analyze the interactions of particle detectors with coherent states of a free scalar field. We find that the eigenvalues of the post-interaction density matrices of i) a single detector, ii) two detectors, and iii) the partial transpose of the latter, are all independent of which coherent state the field was in. A consequence of these results is that a detector pair can harvest the same amount of entanglement from any coherent field state as from the vacuum.
“…This approximation consists of neglecting the dynamics coming from the coupling of the off-resonant modes with the particle detectors. It is easily seen that the effect of the off-resonant modes in the quantum state of a particle detector at leading order in perturbation theory becomes negligible for times much larger than the light-crossing time of the cavity (see, for instance, [24]). …”
We propose a protocol by which entanglement can be extracted repeatedly from
a quantum field. In analogy with prior work on entanglement harvesting, we call
this protocol entanglement farming. It consists of successively sending pairs
of unentangled particles through an optical cavity. Using non-perturbative
Gaussian methods, we show that in certain generic circumstances this protocol
drives the cavity field towards a non-thermal metastable state. This state of
the cavity is such that successive pairs of unentangled particles sent through
the cavity will reliably emerge significantly entangled. We calculate
thermodynamic aspects of the harvesting process, such as energies and
entropies, and also the long-term behavior beyond the few-mode approximation.
Significant for possible experimental realizations is the fact that this
entangling fixed point state of the cavity is reached largely independently of
the initial state in which the cavity was prepared. Our results suggest that
reliable entanglement farming on the basis of such a fixed point state should
be possible also in various other experimental settings, namely with the
to-be-entangled particles replaced by arbitrary qudits and with the cavity
replaced by a suitable reservoir system.Comment: V2: Added Journal Reference. Title modified to match published
version. 16 pages, 8 figures. RevTex 4.
“…Whilst looking at the interaction terms themselves (3), Clerk & Sipe [14] demonstrated that the RWA's nonlocality stems from the RWA interaction Hamiltonian's non-locality, a result that is independent of the field measurment device used. This non-locality can then be quantified by the standard approach in Relativistic Quantum Information where we consider the actual communication between two particle detectors under the Unruh-DeWitt interaction (see, among others, [6,7,[15][16][17][18]).…”
We present new results on the causality violations introduced by the rotating wave approximation commonly used in quantum optics and high-energy physics. We find that the causality violations and faster-than-light signalling induced by the approximation have 'fat tails', i.e., they are polynomially decaying with the distance from the light-cone of the emitter. Furthermore, we also show that the fundamental problems with the incompatibility between the approximation and relativity are not cured even in the long interaction time regime (where the approximation is often taken). This renders the approximation unsuitable for any regime where we are concerned about relativistic causality and information transmission via the electromagnetic field.
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