Squeezing the angular momentum of an ensemble of complex multi-level atoms

Abstract

Squeezing of collective atomic spins has been shown to improve the sensitivity of atomic clocks and magnetometers to levels significantly below the standard quantum limit. In most cases the requisite atom-atom entanglement has been generated by dispersive interaction with a quantized probe field, or by state dependent collisions in a quantum gas. Such experiments typically use complex multilevel atoms like Rb or Cs, with the relevant interactions designed so atoms behave like pseudo-spin-$1/2$ particles. We demonstrate the viability of spin squeezing for collective spins composed of the physical angular momenta of $\sim 10^6$ Cs atoms, each in an internal spin-4 hyperfine state. A peak metrological squeezing of $\gtrsim -5$dB was generated by quantum backaction from a dispersive quantum nondemolition (QND) measurement, implemented using a two-color optical probe that minimizes tensor light shifts without sacrificing measurement strength. Other significant developments include the successful application of composite pulse techniques for accurate dynamical control of the collective spin, enabled by broadband suppression of background magnetic fields inside a state-of-the-art magnetic shield. The absence of classical noise has allowed us to compare the observed quantum projection noise and squeezing to a theoretical model that properly accounts for both the relevant atomic physics and the spatial mode of the collective spin, finding good quantitative agreement and thereby validating its use in other contexts. Thus, our work sets the stage for experiments on quantum feedback, deterministic squeezing, closed-loop magnetometry, and new types of quantum simulation based on continuous QND measurement and feedback.

arXiv comment14 pages, 4 figures

References in corpus (26)

• Quantum metrology with nonclassical states of atomic ensembles
• Atom chip based generation of entanglement for quantum metrology
• Squeezing and entanglement in a Bose-Einstein condensate
• Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit
• States of an Ensemble of Two-Level Atoms with Reduced Quantum Uncertainty
• Spin-Nematic Squeezed Vacuum in a Quantum Gas
• Magnetic sensitivity beyond the projection noise limit by spin squeezing
• Scalable Spin Squeezing for Quantum-Enhanced Magnetometry with Bose-Einstein Condensates
• Entanglement-assisted atomic clock beyond the projection noise limit
• Reduced back-action for phase sensitivity 10 times beyond the standard quantum limit
• Spin squeezing of a cold atomic ensemble with the nuclear spin of one-half
• Continuous Weak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble
• Quantum control and measurement of atomic spins in polarization spectroscopy
• Robust quantum parameter estimation: coherent magnetometry with feedback
• Continuous quantum nondemolition feedback and unconditional atomic spin squeezing
• QND Measurement of Large-Spin Ensembles by Dynamical Decoupling
• Polarization-based Light-Atom Quantum Interface with an All-optical Trap
• A Continuous Non-demolition Measurement of the Cs Clock Transition Pseudo-spin
• Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements
• Simulating nonlinear dynamics of collective spins via quantum measurement and feedback
• Multilevel Holstein-Primakoff approximation and its application to atomic spin squeezing and ensemble quantum memories
• Enhanced squeezing of a collective spin via control of its qudit subsystems
• Three-dimensional light-matter interface for collective spin squeezing in atomic ensembles
• Simulation of complex dynamics of mean-field $p$-spin models using measurement-based quantum feedback control
• Magic-wavelength Faraday probe measures spin continuously and without light shifts
• Enhanced cooperativity for quantum-nondemolition-measurement--induced spin squeezing of atoms coupled to a nanophotonic waveguide

Cited by in corpus (6)

• Emergent dark states from superradiant dynamics in multilevel atoms in a cavity
• Simulation of complex dynamics of mean-field $p$-spin models using measurement-based quantum feedback control
• Crafting the dynamical structure of synchronization by harnessing bosonic multilevel cavity QED
• Spin qudit tomography and state reconstruction error
• Tunable photon-mediated interactions between spin-1 systems
• Multi-state interferometric measurement of nonlinear AC Stark shift