arXiv:2503.09990 · Physical Review Research

Entanglement witness for combined atom interferometer-mechanical oscillator setup

Gayathrini Premawardhana, Deven P. Bowman, Jacob M. Taylor

Published Sep 19, 2025• 0 citations

Abstract

We investigate how to entangle an atom interferometer and a macroscopic mechanical oscillator to create nonclassical states of the oscillator. This work is done in the context of an experimental-theoretical collaboration that aims to implement the proposal in the paper “Using an Atom Interferometer to Infer Gravitational Entanglement Generation,” written by Carney . []. Here, we propose an entanglement witness (EW), from whose violation the generation of entanglement can be determined. We do this for three scenarios: the noiseless case, when including thermal noise, and with atomic dephasing. Thermal noise can arise from two sources: the first being when the oscillator starts in a thermal state, and the second when a continuous thermal bath is in contact with the oscillator. We find that for the appropriate oscillator quality factor Q , violation always exists for any value of coupling λ and thermal occupancy n ¯ . Cooling the oscillator to its ground state provides an O ( n ¯ ) improvement in the EW violation than when starting in a thermal state; in this case, we find that couplings of λ = 10 − 4.5 require at least ∼ 10 5.2 measurements for violation to be observed. For atomic dephasing, we find that EW violation can exist for an atom interferometer with a coherence time of 600 s, which is the parameter our experimental collaborators hope to reach. Finally, we consider how to use magnetic interactions to realize this idea within the context of the torsional pendulum that has been planned for our collaboration.

DOI: 10.1103/rdyx-y8yx

Related papers

Constraints on probing quantum coherence to infer gravitational entanglement

Onur Hosten

Finding a feasible scheme for testing the quantum mechanical nature of the gravitational interaction has been attracting an increasing level of attention. Gravity mediated entanglement generation so far appears to be the key ingredient for a potential experiment. In a recent proposal [D. Carney et al., PRX Quantum 2, 030330 (2021)] combining an atom interferometer with a low-frequency mechanical oscillator, a coherence revival test is proposed for verifying this entanglement generation. With measurements performed only on the atoms, this protocol bypasses the need for correlation measurements. Here, we explore formulations of such a protocol, and specifically find that in the envisioned regime of operation with high thermal excitation, semiclassical models, where there is no concept of entanglement, also give the same experimental signatures. We elucidate in a fully quantum mechanical calculation that entanglement is not the source of the revivals in the relevant parameter regime. We argue that, in its current form, the suggested test is only relevant if the oscillator is nearly in a pure quantum state, and in this regime the effects are too small to be measurable. We further discuss potential open ends. The results highlight the importance and subtleties of explicitly considering how the quantum case differs from the classical expectations when testing for the quantum mechanical nature of a physical system.

arXiv:2106.08221Physical Review ResearchJan 10, 20227 citations

Limits on inference of gravitational entanglement

Yue Ma, Thomas Guff, Gavin W. Morley +2 more

Combining gravity with quantum mechanics remains one of the biggest challenges of physics. In the past years, experiments with optomechanical systems have been proposed that may give indirect clues about the quantum nature of gravity. In a recent variation of such tests [Carney et al., PRX Quantum 2, 030330 (2021)], the authors propose to gravitationally entangle an atom interferometer with a mesoscopic oscillator. The interaction results in periodic drops and revivals of the interferometeric visibility, which under specific assumptions indicate the gravitational generation of entanglement. Here, we study semiclassical models of the atom interferometer that can reproduce the same effect. We show that the core signature---periodic collapses and revivals of the visibility---can appear if the atom is subject to a random unitary channel, including the case where the oscillator is fully classical and situations even without explicit modeling of the oscillator. We also show that the nonclassicality of the oscillator vanishes unless the system is very close to its ground state, and even when the system is in the ground state, the nonclassicality is limited by the coupling strength. Our results thus indicate that deducing entanglement from the proposed experiment is very challenging, since fulfilling and verifying the nonclassicality assumptions constitute a significant challenge in their own right.

arXiv:2111.00936Physical Review ResearchJan 10, 202213 citations

Using an Atom Interferometer to Infer Gravitational Entanglement Generation

Daniel Carney, Holger Müller, Jacob M. Taylor

If gravitational perturbations are quantized into gravitons in analogy with the electromagnetic field and photons, the resulting graviton interactions should lead to an entangling interaction between massive objects. We suggest a test of this prediction. To do this, we introduce the concept of interactive quantum information sensing. This novel sensing protocol is tailored to provable verification of weak dynamical entanglement generation between a pair of systems. We show that this protocol is highly robust to typical thermal noise sources. The sensitivity can moreover be increased both using an initial thermal state and/or an initial phase of entangling via a non-gravitational interaction. We outline a concrete implementation testing the ability of the gravitational field to generate entanglement between an atomic interferometer and mechanical oscillator. Preliminary numerical estimates suggest that near-term devices could feasibly be used to perform the experiment.

Aug 1, 202169 citations

Using an Atom Interferometer to Infer Gravitational Entanglement Generation

Daniel Carney, Holger Müller, Jacob M. Taylor

If gravitational perturbations are quantized into gravitons in analogy with the electromagnetic field and photons, the resulting graviton interactions should lead to an entangling interaction between massive objects.We suggest a test of this prediction.To do this, we introduce the concept of interactive quantum information sensing.This novel sensing protocol is tailored to provable verification of weak dynamical entanglement generation between a pair of systems.We show that this protocol is highly robust to typical thermal noise sources.Moreover, the sensitivity can be increased both using an initial thermal state and/or an initial phase of entangling via a nongravitational interaction.We outline a concrete implementation testing the ability of the gravitational field to generate entanglement between an atomic interferometer and a mechanical oscillator.Preliminary numerical estimates suggest that near-term devices could feasibly be used to perform the experiment.

arXiv:2101.11629PRX QuantumAug 18, 202187 citations

Hybrid Atomic-Optomechanical Systems -- Observing Quantum Effects in Macroscopic Oscillators

Swati Singh

This thesis concentrates on generating and measuring non-classical states of mechanical oscillators by coupling them to atomic and molecular quantum systems. We start with a discussion of what novel physics can be explored by mechanical systems operating in the quantum regime. We then discuss one technique making it a possibility- cavity optomechanics, particularly optomechanical cooling. We investigate the limits of optomechanical cooling and review how the coupling of mechanical oscillators to external heat baths limits the minimum attainable phonon occupation number. As a possible alternative for circumventing clamping losses, we consider an all-optical approach where the mechanical element (in this case, a Bragg mirror) is suspended via optical forces, and discuss some limitations of this approach. We explore several schemes aimed at the generation of quantum states in mechanical oscillators. We consider specifically two examples: one in which the mechanical oscillator is coupled to polar molecules via dipole-dipole interaction, and another where it is magnetically coupled to a Bose condensate. The first example emphasizes that such an interaction can generate parametric squeezing and entanglement. The second scheme demonstrates that the back action of BEC spin measurements can be used to generate quantum states of motion of a mechanical oscillator. We then discuss possible methods for measuring the entire density matrix of a mechanical oscillator. The first method achieves the tomographic reconstruction of the mechanical Wigner function by coupling it simultaneously to a classical optical oscillator and a qubit. The second approach involves a state transfer scheme between momentum excitations of a bose-condensate in a cavity and a moving mirror of the cavity that is entirely mediated by the light field. We conclude with a discussion of the broader implications of this work, and some future research directions.

Jan 1, 20120 citations

Enforcing nonclassicality in medium-scale quantum systems

Hannah McAleese

This thesis investigates three aspects of nonclassicality. The first aspect is macroscopic quantumness, a field which considers the properties of macroscopic superpositions. The various measures of macroscopicity are reviewed. An optomechanical system is described which enables us to study nonclassicality in macroscopic mechanical oscillators. We analyse the impact of different measurement settings on the macroscopicity of the mirror and the Wigner functions of the mechanical state. The same system is also considered under open system dynamics. The second nonclassical concept is the violation of macrorealism. It is shown that a two-level system can violate the Leggett-Garg inequality, thereby demonstrating that the assumptions of macrorealism do not hold. Similar dynamics are then replicated in a macroscopic mechanical system through the use of a hybrid optomechanical system in which an atom interacts with the mechanical oscillator through an optical mode. Mechanical damping is then factored into the dynamics to examine its effect on the violation of the Leggett-Garg inequality for different parameter ranges. The third is nonclassical correlations. Quantum discord and quantum entanglement are defined and several measures are explained. Entanglement distribution via separable states is introduced and then built on by adding imperfections to the operations in the protocol. It is found that the protocol is still successful in spite of the errors in the operations, both when they are unitary and non-unitary. We also develop a method of generating entanglement between two bosons through mediation with two spin systems. Through this system we demonstrate the creation of both entangled coherent states and NOON states.

Oct 1, 20260 citations