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arXiv:1912.04039 · Nanophotonics

Strong spin squeezing induced by weak squeezing of light inside a cavity

Wei Qin, Ye‐Hong Chen, Xin Wang, Adam Miranowicz, Franco Nori

Published Jun 1, 2018• 44 citations
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Abstract

Abstract We propose a simple method for generating spin squeezing of atomic ensembles in a Floquet cavity subject to a weak, detuned two‐photon driving. We demonstrate that the weak squeezing of light inside the cavity can, counterintuitively, induce strong spin squeezing . This is achieved by exploiting the anti‐Stokes scattering process of a photon pair interacting with an atom. Specifically, one photon of the photon pair is scattered into the cavity resonance by absorbing partially the energy of the other photon whose remaining energy excites the atom . The scattering, combined with a Floquet sideband, provides an alternative mechanism to implement Heisenberg‐limited spin squeezing. Our proposal does not need multiple classical and cavity‐photon drivings applied to atoms in ensembles, and therefore its experimental feasibility is greatly improved compared to other cavity‐based schemes. As an example, we demonstrate a possible implementation with a superconducting resonator coupled to a nitrogen‐vacancy electronic‐spin ensemble.

DOI
10.1515/nanoph-2020-0513

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Abstract We propose a simple method for generating spin squeezing of atomic ensembles in a Floquet cavity subject to a weak, detuned two‐photon driving. We demonstrate that the weak squeezing of light inside the cavity can, counterintuitively, induce strong spin squeezing . This is achieved by exploiting the anti‐Stokes scattering process of a photon pair interacting with an atom. Specifically, one photon of the photon pair is scattered into the cavity resonance by absorbing partially the energy of the other photon whose remaining energy excites the atom . The scattering, combined with a Floquet sideband, provides an alternative mechanism to implement Heisenberg‐limited spin squeezing. Our proposal does not need multiple classical and cavity‐photon drivings applied to atoms in ensembles, and therefore its experimental feasibility is greatly improved compared to other cavity‐based schemes. As an example, we demonstrate a possible implementation with a superconducting resonator coupled to a nitrogen‐vacancy electronic‐spin ensemble.
Spin-spin interactions generated by a detuned cavity are a standard mechanism for generating highly entangled spin squeezed states. We show here how introducing a weak detuned parametric (two-photon) drive on the cavity provides a powerful means for controlling the form of the induced interactions. Without a drive, the induced interactions cannot generate Heisenberg-limited spin squeezing, but a weak optimized drive gives rise to an ideal two-axis twist interaction and Heisenberg-limited squeezing. Parametric driving is also advantageous in regimes limited by dissipation, and enables an alternate adiabatic scheme which can prepare optimally squeezed, Dicke-like states. Our scheme is compatible with a number of platforms, including solid-state systems where spin ensembles are coupled to superconducting quantum circuits or mechanical modes.
It has been shown elsewhere that two spatially separated atoms can jointly absorb one photon, whose frequency is equal to the sum of the transition frequencies of the two atoms. We describe this process in the presence of an ensemble of many two-level atoms and show that it can be used to generate spin squeezing and entanglement. This resonant collective process allows us to create a sizable squeezing already at the single-photon limit. It represents a way to generate many-body spin-spin interactions, yielding a two-axis twisting-like interaction among the spins, which is very efficient for the generation of spin squeezing. We perform explicit calculations for ensembles of magnetic molecules coupled to a superconducting coplanar cavities. This system represents an attractive on-chip architecture for the realization of improved sensing.
An advantageous architecture for producing deterministic spin squeezing is cavity QED. We show that the recently discovered one photon - two atom excitation process can be used to generate optimal squeezing (scaling as 1/N1/N1/N) of an ensemble of NNN spins coupled to a single-mode cavity. This method has some remarkable features. It is a resonant phenomenon mediated by real photons, which provides the advantage of tunability. This allows to create a sizeable squeezing already at the single-photon limit. Finally, in the strong cavity-driving regime the effective theory is similar to a two-axis Hamiltonian. We calculate that reaching −30-30−30dB is possible already with the known reported spin-cavity and decoherence rates in magnetic molecules coupled to superconducting circuit resonators. This system represents an attractive on-chip architecture for the realization of technological solutions in sensing.
The antibunching effect generated in a cavity containing first a single two-level atomic system and then two identical atoms is explored for off-resonant interactions, in strong- and weak-coupling regimes. The cavity is driven by coherent and squeezed sources. Using the second-order correlation function analytically derived in the weak-excitation regime, we show that squeezed light achieves and improves strong antibunching, leading to a photon blockade. This enhancement is due to a destructive quantum interference mechanism induced by the nonclassical light, creating a supplementary transition pathway. The best effect is obtained for equal frequency detunings in the strong-coupling regime. More interestingly, our investigation reveals that the two-atom-cavity system can further improve the antibunching effect compared to the single-atom cavity. It turns out that the additional couplings appearing in the cavity due to the implementation of the two atoms, combined with the squeezed light, could substantially enhance the photon-blockade effect.
Spin squeezing has important applications in the field of quantum metrology and quantum information processing. Here we propose that coherent population trapping is well suitable for establishing cavity dissipation mechanism and generating a spin-squeezed state. An ensemble of N double Λ -type atoms is placed inside the two-mode optical cavity, where one Λ subsystem is driven resonantly by two strong control fields to form a dark resonance and the other Λ subsystem is coupled by two cavity vacuum fields and two external fields with large detunings. Due to the dark resonance, the atoms are trapped in a dark state and one has the maximal coherence between the two ground states. Two double off-resonance stimulated Raman scattering interactions are induced between fields and dressed atoms to establish a dissipative quantum dynamical process based on a collective cavity reservoir. As a result, strong stable spin squeezing is generated, which is verified by our numerical and analytical results. Published by the American Physical Society 2024
Squeezed spin states have important applications in quantum metrology and sensing. It has been shown by S\o{}rensen and M\o{}lmer [Phys. Rev. A 66, 022314 (2002)] that an effective one-axis-twisting interaction can be realized in a cavity setup via a double off-resonance stimulated Raman scattering, resulting in a noise reduction scaling $\ensuremath{\propto}1/{N}^{2/3}$ with NNN being the atom number. Here, we show that, by making an appropriate change of the initial input spin state, it is possible to produce a one-axis-twisting spin squeezing via a single off-resonance stimulated Raman scattering, which thus can greatly simplify the realistic implementation. We also show that the one-axis-twisting interaction can be transformed into a more efficient two-axis-twisting interaction by rotating the collective spin while coupling to the cavity, yielding a Heisenberg limited noise reduction $\ensuremath{\propto}1/N$. Considering the noise effects due to atomic decoherence and cavity decay, we find that substantial squeezing is still attainable with current laboratory techniques.