Force sensors with precision beyond the standard quantum limit

Abstract

We propose force sensing protocols using linear ion chain which can operate beyond the quantum standard limit. We show that oscillating forces that are off-resonance with the motional trap frequency can be detected very efficiently by using quantum probes represented by various spin-boson models. We demonstrate that the temporal evolution of a quantum probe described by the Dicke model can be mapped on the nonlinear Ramsey interferometry which allows to detect far-detuned forces simply by measuring the collective spin populations. Moreover, we show that the measurement uncertainty can reach the Heisenberg limit by using initial spin correlated states, instead of motional entangled states. An important advantage of the sensing technique is its natural robustness against the thermally induced dephasing, which extends the coherence time of the measurement protocol. Furthermore, we introduce sensing scheme that utilize the strong spin-phonon coupling to improve the force estimation. We show that for quantum probe represented by quantum Rabi model the force sensitivity can overcome those using simple harmonic oscillator as a force sensor.

Efficient approach for quantum sensing field gradients with trapped ions

“…An estimation of the force magnitude via detecting the mean phonon number with single trapped ion was discussed in [12]. Here we show that the force difference caused excitation of phonons in the collective rocking mode while the mean phonon number of the collective center-of-mass mode is proportional to the total force along the trap axis.…”

Enhanced Parameter Estimation with Periodically Driven Quantum Probe

“…A different class of phase transitions was introduced in an interacting system of single-mode cavity field and two-level atom, where the thermodynamic limit requires the cavity frequency in units of atomic transition frequency to tend to zero [11,12]. An enhanced parameter estimation was proposed with such finite size critical quantum optical system for high-precision force measurements [13][14][15] or frequency measurements [8,9]. The corresponding quantum Fisher information diverges by approaching the critical coupling, indicating that the finite size quantum optical system becomes sensitive to infinitely small variation of the parameter of interest.…”

Enhanced Parameter Estimation with Periodically Driven Quantum Probe

“…A different class of phase transitions was introduced in an interacting system of single-mode cavity field and two-level atom, where the thermodynamic limit requires the cavity frequency in units of atomic transition frequency to tend to zero [9,10]. An enhanced parameter estimation was proposed with such finite size critical quantum optical system for high-precision force measurements [11][12][13] or frequency measurements [6,7]. The corresponding quantum Fisher information diverges by approaching the critical coupling indicating that the finite size quantum optical system becomes sensitive to infinitely small variation of the parameter of interest.…”