Generating entanglement between atomic spins with low-noise probing of an optical cavity

Abstract

Atomic projection noise limits the ultimate precision of all atomic sensors, including clocks, inertial sensors, magnetometers, etc. The independent quantum collapse of N atoms into a definite state (for example spin up or down) leads to an uncertainty ∆θSQL = 1/ √ N in the estimate of the quantum phase accumulated during a Ramsey sequence or its many generalizations. This phase uncertainty is referred to as the standard quantum limit. Creating quantum entanglement between the N atoms can allow the atoms to partially cancel each other's quantum noise, leading to reduced noise in the phase estimate below the standard quantum limit. Recent experiments have demonstrated up to 10 dB of phase noise reduction relative to the SQL by making collective spin measurements. This is achieved by trapping laser-cooled Rb atoms in an optical cavity and precisely measuring the shift of the cavity resonance frequency by an amount that depends on the number of atoms in spin up. Detecting the probe light with high total efficiency reduces excess classical and quantum back-action of the probe.Here we discuss recent progress and a technique for reducing the relative frequency noise between the probe light and the optical cavity, a key requirement for further advances. arXiv:1504.05160v1 [physics.atom-ph]

Assessment of Rydberg atoms for wideband electric field sensing

“…Our implementation follows that of Ref. [51] where we simultaneously measure an optical heterodyne with a sideband of the probe to stabilize the relative beam path phase. This method has the advantage of an easy change between measurement quadratures without the need for a second reference laser.…”

“…Our implementation follows a modification used in Ref. [51]. A single laser sent through acousto-optic modulators (AOMs) creates both the probe and reference beams; a subsequent electro-optic modulator (EOM) places sidebands on the probe beam such that the lower sideband is equal in frequency to the reference.…”

“…The transmitted probe light is measured using an optical homodyne method similar to those in [3,49] which allows for precise, photon-shot-noise limited measurements in both the phase and amplitude quadratures. Our implementation follows a modification used in [50]. A single laser sent through acousto-optic modulators creates both the probe and reference beams; a subsequent electro-optic modulator places sidebands on the probe beam such that the lower sideband is equal in frequency to the reference.…”

Quantum metrology with mixed states: When recovering lost information is better than never losing it

“…When system B is a photon field andĤ B is proportional to the number of photons in the field, thenĤ AB describes the weak probing of the population difference of an ensemble of two-level atoms with far-detuned light [37,[52][53][54][55][56][57][58][59][60][61], or dispersive coupling between a microwave cavity and a superconducting qubit [62][63][64]. We will explore this specific case shortly, however, for now we keepĤ B completely general.…”