Gravitational decoherence

Abstract

We investigate the effect of quantum metric fluctuations on qubits that are gravitationally coupled to a background spacetime. In our first example, we study the propagation of a qubit in flat spacetime whose metric is subject to flat quantum fluctuations with a Gaussian spectrum. We find that these fluctuations cause two changes in the state of the qubit: they lead to a phase drift, as well as the expected exponential suppression (decoherence) of the off-diagonal terms in the density matrix. Secondly, we calculate the decoherence of a qubit in a circular orbit around a Schwarzschild black hole. The no-hair theorems suggest a quantum state for the metric in which the black hole's mass fluctuates with a thermal spectrum at the Hawking temperature. Again, we find that the orbiting qubit undergoes decoherence and a phase drift that both depend on the temperature of the black hole. Thirdly, we study the interaction of coherent and squeezed gravitational waves with a qubit in uniform motion. Finally, we investigate the decoherence of an accelerating qubit in Minkowski spacetime due to the Unruh effect. In this case decoherence is not due to fluctuations in the metric, but instead is caused by coupling (which we model with a standard Hamiltonian) between the qubit and the thermal cloud of Unruh particles bathing it. When the accelerating qubit is entangled with a stationary partner, the decoherence should induce a corresponding loss in teleportation fidelity.

Methods of approaching decoherence in the flavor sector due to space-time foam

“…The most satisfactory way of dealing with the effects of such a background is by coupling covariantly the gravitational field to a Klein-Gordon or Dirac lagrangian.This avoids intuitive arguments which are sometimes presented [27] and correctly incorporates covariance unlike these other approaches.…”

“…We will consider the neutrino to be moving in the x-direction. For simplicity [27] we will examine the situation where the relevant part of the contravariant metric can be regarded as being in 1 + 1 dimension.…”

Resonance interaction energy between two accelerated identical atoms in a coaccelerated frame and the Unruh effect

“…Initially treated as a purely kinematic effect, the Unruh effect has stimulated intense theoretical investigations on the dynamical properties of uniformly accelerated systems, for example the emission of radiation from uniformly accelerated atoms [5]. The importance of the Unruh effect is nowadays recognized, not only in its own right, but also in connection with many other actual research topics, such as black hole evaporation [6], cosmological horizon [7], and also applications in quantum information science [8,9]. Several experimental schemes have been proposed to detect this very tiny effect, intertwining quantum physics and general relativity, in the laboratory, but it has not been yet observed.…”

Changing quantum reference frames

“…With a construction and characterisation of a 'change of quantum reference frame' procedure, we quantitatively investigate the decoherence resulting from changing physical quantum reference frames. We interpret this appearance of decoherence in terms of a type of intrinsic decoherence, which is a proposed semiclassical phenomenon of quantum gravity arising from fundamental uncertainties in the background space [16][17][18][19][20][21].…”