Entanglement-Enhanced Matter-Wave Interferometry in a High-Finesse Cavity

Abstract

Entanglement is a fundamental resource that allows quantum sensors to surpass the standard quantum limit set by the quantum collapse of independent atoms. Collective cavity-QED systems have succeeded in generating large amounts [1,2] of directly observed entanglement involving the internal degrees of freedom of laser-cooled atomic ensembles [1][2][3][4][5][6][7][8][9][10][11][12]. Here we demonstrate cavity-QED entanglement of external degrees of freedom to realize a matter-wave interferometer of 700 atoms in which each individual atom falls freely under gravity and simultaneously traverses two paths through space while also entangled with the other atoms. We demonstrate both quantum non-demolition measurements and cavity-mediated spin interactions for generating squeezed momentum states with directly observed metrological gain 3.4 +1.1 −0.9 dB and 2.5 +0.6 −0.6 dB below the standard quantum limit respectively. An entangled state is successfully injected into a Mach-Zehnder light-pulse interferometer with 1.7 +0.5 −0.5 dB of directly observed metrological enhancement. These results open a new path for combining particle delocalization and entanglement for inertial sensors [13,14], searches for new physics, particles, and fields [15-21], future advanced gravitational wave detectors [22][23][24], and accessing beyond mean-field quantum many-body physics [25][26][27][28][29].

Multi-photon Atom Interferometry via cavity-enhanced Bragg Diffraction

“…[31] of a 2 k cavity atom interferometer was realized in a configuration where atoms are trapped efficiently in the small mode volume (600 µm) of a stable resonator. In a more recent work, a stable high finesse optical cavity was used for entanglement enhancement of atom interferometry [16].…”

“…This new generation of high precision detectors share a common philosophy: a network of atom interferometers are simultaneously interrogated by the same optical pulse. Various techniques are proposed, in combination, to reach the projected sensitivity required for these high precision tests -bright atomic flux [12,13], interleaved interferometers [14], entangled sources [15,16], but also large momentum transfer (LMT) atom optics. In such experiments, the sensitivity of the measurement fundamentally depends on the spatial separation of matter waves inside the interferometer, which is commonly limited by the use of 2-photon momentum transfer from the interrogation field to the atoms.…”

Light-pulse atom interferometry with entangled atom-optical elements

“…However, we only discussed a first-quantized matter wave. The nonlinear interaction and entanglement of secondquantized many-particle atomic and optical fields are expected to enhance the interferometric sensitivity beyond the shot-noise limit [28][29][30][31][32][33]. Thus, we expect further studies of quantized beam splitters and mirrors acting on second-quantized atomic systems to demonstrate a true metrological gain.…”

“…Besides these single-atom considerations, Raman superradiant transitions [26,27] or diffraction from optical cavities with quantized light fields are one promising route to generate quantum states with metrological gain for atom interferometry [28,29]. The sensitivity of atom interferometers can be enhanced even further if one performs measurements on the diffracting light fields [30][31][32][33], thus recycling the information.…”

Laser frequency offset locking at 10-Hz-level instability using hybrid electronic filters

“…A direct beat note between two lasers can be detected up to tens of GHz on fast photodiodes, and offsets up to a couple of hundred GHz is achievable by beating one of the lasers with a high-order sideband of another laser resulting from its phase modulation with an EOM [16]. All the way up to octave-spanning THz offset frequencies can be achieved by utilizing the beat notes of two lasers with different spectral lines of an optical frequency comb [17], enabling optical clock frequency comparison.…”