Recently a certain thought experiment was discussed which involves the decoherence of a quantum system due to a black hole. Here we show how this phenomenon is consistent with standard ideas about quantum black holes. In other words, modeling the black hole as a quantum system at finite temperature one obtains the same answer. We demonstrate this by analyzing the problem in terms of an effective theory that can apply both for the black hole case and for an ordinary matter system, showing that the same qualitative effect is present for ordinary matter at finite temperature.
Recently a certain thought experiment was discussed which involves the decoherence of a quantum system due to a black hole. Here we show how this phenomenon is consistent with standard ideas about quantum black holes. In other words, modeling the black hole as a quantum system at finite temperature one obtains the same answer. We demonstrate this by analyzing the problem in terms of an effective theory that can apply both for the black hole case and for an ordinary matter system, showing that the same qualitative effect is present for ordinary matter at finite temperature.
A bstract In this note, we reexamine decoherence effects in quantum field theories with gravity duals. The thought experiment proposed in [1, 2], which reveals novel decoherence patterns associated with black holes, also manifests itself from the perspective of the boundary theory. In particular, we consider a moving mirror coupled to quantum critical theories characterized by a dynamical exponent z that are dual to asymptotically Lifshitz geometries. The interference experiment occurs on the boundary, where a superposition of two spatially separated quantum states of a mirror is maintained for a finite time τ 0 before recombination. We find that the interaction with a quantum field at finite temperature, arising from the presence of a Lifshitz black hole, leads to a constant decoherence rate. In contrast, for the zero-temperature case corresponding to pure Lifshitz spacetime, the decoherence rate vanishes in the large-time limit τ 0 → ∞. Remarkably, in the zero-temperature regime, the decoherence exhibits a power-law decay at large τ 0 as z → ∞, a behavior reminiscent of the decoherence patterns seen in extremal black hole geometries. In addition, we investigate the decoherence of one particle in an EPR pair constructed holographically. Our results indicate that causality plays a crucial role in determining whether the entanglement leads to the suppression of decoherence in the other particle.
We study the decoherence induced by near-extremal charged black holes on quantum systems in their exterior. Specifically, we analyze a thought experiment recently discussed in the literature, where the quantum system is a charged particle prepared in a spatial superposition. Near-extremal black holes are known to exhibit large quantum metric fluctuations of the near-horizon geometry at low temperatures. We show that, at late times, if the black hole is sufficiently close to extremality, these quantum gravity effects make the decoherence rate vanish. This phenomenon is due to a spin-induced energy gap in the quantum black hole spectrum. For energies above the gap, the decoherence rate becomes nonzero, but is still suppressed relative to semiclassical expectations, so these quantum gravity effects always enhance the coherence of the superposition.
Recently, it has been shown that a quantum system held in spatial superposition and then eventually recombined does experience decoherence from black hole horizons, at a level increasing linearly with the time the superposition has been kept open. In this, the effects of the horizon have been derived using a classical spacetime picture for the latter. In the present paper we point out that quantum aspects of the geometry itself of the quantum black hole could significantly affect the results. In a specific effective implementation of the quantum geometry in terms of a minimal length and ensuing minimal area, it appears in particular that, for selected values of the quantum of area proposed on various grounds in the literature, the decoherence induced by the horizon turns out to be limited to negligibly small values.
There is mounting theoretical evidence that black hole horizons induce decoherence on a quantum system, say a particle, put in a superposition of locations, with the decoherence functional, evaluated after closure of the superposition, increasing linearly with the time the superposition has been kept open. This phenomenon has been shown to owe its existence to soft modes, that is modes with very low frequencies, of the quantum fields---sourced by the particle---which pierce through the horizon, or also can be understood as coming from the interaction with the black hole described as a thermodynamic quantum system at Hawking's temperature. Here we investigate the effects of ensuing quantum aspects of the geometry itself of the horizon, in an effective perspective in which the quantum geometry of the horizon is captured by the existence of a limit length or by a horizon area quantization. We show that the discreteness of the energy levels associated to the different geometric configurations might have a strong impact on the results, in particular reducing the decoherence effects even to a negligible level in the case of quanta of area A0=O(1)lp2 or larger, with lp the Planck length.
Recently, it was shown by Danielson (DSW) that, for the massive or charged body in a quantum spatial separated superposition state, the presence of a black hole can decohere the superposition inevitably toward capturing the radiation of soft photons or gravitons [D. L. Danielson , Black holes decohere quantum superpositions, ; D. L. Danielson , Killing horizons decohere quantum superpositions, ; D. L. Danielson , Local description of decoherence of quantum superpositions by black holes and other bodies, ]. In this work, we study the DSW decoherence effect for the static charged body in the Reissner-Nordström black holes. By calculating the decohering rate for this case, it is shown that the superposition is decohered by the low-frequency photons that propagate through the black hole horizon. For the extremal Reissner-Nordström black hole, the decoherence of quantum superposition is completely suppressed due to the black hole Meissner effect. It is also found that the decoherence effect caused by the Reissner-Nordström black hole is equivalent to that of an ordinary matter system with the same size and charge.
An environment interacting with a system acquires information about it, e.g. about its location. The resulting decoherence is thought to be responsible for the emergence of the classical realm of our Universe out of the quantum substrate. However, this view of the emergence of the classical is sometimes dismissed as a consequence of insufficient isolation and, hence, as non-fundamental. In contrast to many other systems, a black hole can never be isolated from its Hawking radiation which carries information about its location, making this lack of isolation fundamental. Here we consider the decoherence of a "black hole Schrödinger cat"-a non-local superposition of a Schwarzschild black hole in two distinct locations-due to its Hawking radiation. The resulting decoherence rate turns out to be given by a surprisingly simple equation. Moreover, and in contrast to known cases of decoherence, this rate does not involve Planck's constant ħ.