Gravity in the quantum lab

Abstract

At the beginning of the previous century, Newtonian mechanics was advanced by two new revolutionary theories, Quantum Mechanics (QM) and General Relativity (GR). Both theories have transformed our view of physical phenomena, with QM accurately predicting the results of experiments taking place at small length scales, and GR correctly describing observations at larger length scales. However, despite the impressive predictive power of each theory in their respective regimes, their unification still remains unresolved. Theories and proposals for their unification exist but we are lacking experimental guidance towards the true unifying theory. Probing GR at small length scales where quantum effects become relevant is particularly problematic but recently there has been a growing interest in probing the opposite regime, QM at large scales where relativistic effects are important. This is principally because experimental techniques in quantum physics have developed rapidly in recent years with the promise of quantum technologies. Here we review recent advances in experimental and theoretical work on quantum experiments that will be able to probe relativistic effects of gravity on quantum properties. In particular, we emphasise the importance of using the framework of Quantum Field Theory in Curved Spacetime (QFTCS) in describing these experiments. For example, recent theoretical work using QFTCS has illustrated that these quantum experiments could also be used to enhance measurements of gravitational effects, such as Gravitational Waves (GWs). Verification of such enhancements, as well as other QFTCS predictions in quantum experiments, would provide the first direct validation of this limiting case of quantum gravity. ARTICLE HISTORY

Frequency spectrum of an optical resonator in a curved spacetime

“…In such experimental situations, the model we used will certainly not be fully valid and the effects have to be calculated for the precise apparatus that is used. However, the results of this article can serve as a basis for investigations of the accessibility of spacetime parameters and parameters of states of motion in the more advanced framework of quantum metrology [16].…”

“…For example, the frequency spectrum of a resonator depends on its dimensions and hence knowledge of the precise values of these dimensions is of utmost importance. Cases in which the effects of gravitational fields and acceleration must be considered include those in which the gravitational field is to be measured, such as in proposals for the measurement of gravitational waves with electromagnetic cavity resonators [1][2][3][4][5][6][7] or other extended matter systems [8][9][10][11][12][13][14], tests of GR [15,16] or the expansion of the universe [17,18]. Other situations are those in which the metrological system is significantly accelerated [19][20][21].…”

Dynamical response of Bose–Einstein condensates to oscillating gravitational fields

“…in first order in the potential perturbation. Taking this into account, taking the first time derivative of equation (13) and using equation (14) to replaceḟ n , we obtain for each n…”

“…One specific example is the measurement of the thermal Casimir-Polder force [7], which was theoretically proposed in [8]. Further theoretical proposals to use collective oscillations in BECs and, in particular, their phonon modes for sensing purposes include, for example, gravitational wave detectors [9][10][11] , sensors for the effect of spacetime curvature on entanglement [12] (for a review see [13]) and magnetic field and rotation sensors employing solitons formed by optical lattices [14].…”

Entanglement dynamics of two mesoscopic objects with gravitational interaction

“…In that sense, one can prove entanglement between particles in a device-independent way. For simplicity we ignore the fluctuations in the experimental parameters in this section so that the density operator is of the simple form as in equation (8). To see whether ρ violates the CHSH inequality for certain measurement settings, we make use of the criterion described in Ref.…”