Macroscopic superpositions and gravimetry with quantum magnetomechanics

Abstract

Precision measurements of gravity can provide tests of fundamental physics and are of broad practical interest for metrology. We propose a scheme for absolute gravimetry using a quantum magnetomechanical system consisting of a magnetically trapped superconducting resonator whose motion is controlled and measured by a nearby RF-SQUID or flux qubit. By driving the mechanical massive resonator to be in a macroscopic superposition of two different heights our we predict that our interferometry protocol could, subject to systematic errors, achieve a gravimetric sensitivity of Δg/g ~ 2.2 × 10−10 Hz−1/2, with a spatial resolution of a few nanometres. This sensitivity and spatial resolution exceeds the precision of current state of the art atom-interferometric and corner-cube gravimeters by more than an order of magnitude, and unlike classical superconducting interferometers produces an absolute rather than relative measurement of gravity. In addition, our scheme takes measurements at ~10 kHz, a region where the ambient vibrational noise spectrum is heavily suppressed compared the ~10 Hz region relevant for current cold atom gravimeters.

Journeys from quantum optics to quantum technology

“…This work showed the in-principle feasibility (in-theory), to trap and cool the motion of a large levitated object. More recently we developed this concept further to use the quantum magnetic fields produced by a superconducting flux qubit to force the magnetically levitated body into a macroscopic quantum spatial superposition [280]. Using this additional leverage we showed how to implement a type of matter-wave interferometery which used the entire mass of the levitated object to perform absolute measurements of the local acceleration of gravity -or an absolute gravimeter.…”

Quantum sensing with nanoparticles for gravimetry: when bigger is better

“…Proposals combining levitated particles with twolevel-systems include levitated nanodiamonds with an embedded nitrogen-vacancy (NV) centre with an electron spin [68][69][70][71][72], and a superconducting ring resonator coupled to a qubit [73]. Here, we consider stationary spatial superpositions of a levitated nanoparticle oscillator with embedded spin, which remains trapped by an optical tweezer throughout the sensing protocol, as illustrated in Figure 3(A).…”

“…The first pulse introduces Rabi oscillations between the spin eigenvalue states S z +1 and S z −1, such that when a magnetic field gradient is applied the oscillator wavepacket is delocalized. This spin-dependent spatial shift is given by ±Δz g nv μ B Bz 2mΩ 2 , where B z is the magnetic field gradient along the z-direction, which is the same direction that gravity acts in [70,73] 4 , g nv ≈ 2 is the Landé g factor and μ B is the Bohr magneton. This effectively splits the harmonic trapping potential, creating a spatial superposition with equilibrium positions governed by a spindependent acceleration.…”

Large spatial Schrödinger cat state using a levitated ferrimagnetic nanoparticle

“…After levitation, the center-of-mass (CM) temperature T cm of the particle is reduced to mK level using parametric feedback cooling [32]. Here, one can use a superconducting quantum interference device for the detection and the manipulation of the CM motion of the levitated particle [35,36]. Furthermore, we assume that S is an integer to ensure that tunneling between two wells, discussed below, is permissible [37].…”