Testing Quantum Mechanics in a Mechanical System: Characterizing Mechanical Resonators

Björn Schrinski, Yu Yang, Uwe von Lüpke +5 more

Recently, solid-state mechanical resonators have become a platform for demonstrating nonclassical behavior of systems involving a truly macroscopic number of particles. Here, we perform the most macroscopic quantum test in a mechanical resonator to date, which probes the validity of quantum mechanics by ruling out a classical description at the microgram mass scale. This is done by a direct measurement of the Wigner function of a high-overtone bulk acoustic wave resonator mode, monitoring the gradual decay of negativities over tens of microseconds. While the obtained macroscopicity of μ=11.3 is on par with state-of-the-art atom interferometers, future improvements of mode geometry and coherence times could test the quantum superposition principle at unprecedented scales and also place more stringent bounds on spontaneous collapse models.

Hiroshi Yamaguchi

Massimiliano Rossi, David Mason, Junxin Chen +2 more

Germain Tobar, Stefan Forstner, Arkady Fedorov +1 more

Abstract Theories of spontaneous wavefunction collapse offer an explanation of the possible breakdown of quantum mechanics for macroscopic systems. However, the challenge of resolving predicted collapse signatures above background noise has precluded conclusive tests. Here, we propose to overcome this challenge using quantum control and measurement of a superconducting qubit coupled to a macroscopic mechanical resonator. We show that this can amplify the weak signals from collapse-induced heating and simultaneously suppress qubit noise, initializing the qubit close to its ground state. Combined, this could enable a conclusive test of collapse models. The ability to quantum control macroscopic mechanical resonators and resolve extremely small signals from them could further other fundamental research beyond collapse models, such as laboratory-based dark matter searches and the reconciliation of quantum mechanics with gravity.

Lydia A. Kanari-Naish, Jack Clarke, Michael Ross Vanner +1 more

Testing the limits of the applicability of quantum mechanics will deepen our understanding of the universe and may shed light on the interplay between quantum mechanics and gravity. At present there is a wide range of approaches for such macroscopic tests spanning from matter-wave interferometry of large molecules to precision measurements of heating rates in the motion of micro-scale cantilevers. The “displacemon” is a proposed electromechanical device consisting of a mechanical resonator flux-coupled to a superconducting qubit enabling generation and readout of mechanical quantum states. In the original proposal, the mechanical resonator was a carbon nanotube, containing 106 nucleons. Here, in order to probe quantum mechanics at a more macroscopic scale, we propose using an aluminum mechanical resonator on two larger mass scales, one inspired by the Marshall–Simon–Penrose–Bouwmeester moving-mirror proposal, and one set by the Planck mass. For such a device, we examine the experimental requirements needed to perform a more macroscopic quantum test and thus feasibly detect the decoherence effects predicted by two objective collapse models: Diósi–Penrose and continuous spontaneous localization. Our protocol for testing these two theories takes advantage of the displacemon architecture to create non-Gaussian mechanical states out of equilibrium with their environment and then analyzes the measurement statistics of a superconducting qubit. We find that with improvements to the fabrication and vibration sensitivities of these electromechanical devices, the displacemon device provides a new route to feasibly test decoherence mechanisms beyond standard quantum theory.

P.M. Clark, J.E. Turner