[Paper Review] Manipulation and storage of optical field and atomic ensemble quantum states

Aurélien Dantan, Alberto Bramati+2 more|ArXiv.org|Jul 28, 2004

Cold Atom Physics and Bose-Einstein Condensates3 citations

TL;DR

This paper presents a quantum model for non-dissipative, high-efficiency transfer of optical field quantum states—such as squeezed vacuum and Einstein-Podolsky-Rosen (EPR) entangled states—into and out of atomic ensemble spin states using cavity-based electromagnetically induced transparency (EIT) and Raman coupling. The key result is quasiperfect storage and retrieval of quantum states with high fidelity, though direct squeezing transfer between ensembles is limited to ~50% efficiency, requiring quantum teleportation for full transfer.

ABSTRACT

We study how to efficiently manipulate and store quantum information between optical fields and atomic ensembles. We show how various non-dissipative transfer schemes can be used to transfer and store quantum states such as squeezed vacuum states or entangled states into the long-lived ground state spins of atomic ensembles.

Motivation & Objective

• To develop a theoretical framework for non-dissipative, reversible quantum state transfer between optical fields and atomic ensemble spin states.
• To enable long-lived storage of non-classical optical states—such as squeezed vacuum and EPR-entangled states—into collective atomic spin degrees of freedom.
• To investigate the feasibility of transferring quantum correlations (e.g., squeezing) from one atomic ensemble to another for scalable quantum networks.
• To assess the efficiency and fidelity of state transfer under realistic decoherence and loss conditions, particularly for continuous-variable quantum information.
• To identify limitations in direct squeezing transfer between ensembles and propose solutions via quantum teleportation protocols.

Proposed method

• Uses a cavity-coupled Λ-type three-level atomic ensemble model with collective spin operators and field operators governed by Heisenberg-Langevin equations.
• Applies electromagnetically induced transparency (EIT) and off-resonant Raman processes to mediate coherent, non-dissipative coupling between optical fields and atomic ground state coherences.
• Models the system using Langevin noise terms to account for cavity decay (κ), atomic spontaneous emission (γ), and long-lived ground state coherence decay (γ₀).
• Derives input-output relations for cavity fields to describe the readout of stored atomic states into optical fields with high fidelity.
• Introduces a time-domain and Fourier-domain analysis of spin dynamics to evaluate the spectral response and noise transfer during state mapping.
• Proposes a pseudo-quantum repeater scheme using sequential optical readout and write-in operations to transfer squeezing from one ensemble to another via the field mode.

Experimental results

Research questions

• RQ1 Can non-classical optical field states such as squeezed vacuum and EPR-entangled states be efficiently and reversibly mapped onto long-lived atomic spin states?
• RQ2 What is the maximum fidelity and efficiency of quantum state transfer between optical fields and atomic ensembles under realistic decoherence (γ₀)?
• RQ3 To what extent can the squeezing of one atomic ensemble be transferred to a second via an intermediate optical field?
• RQ4 Why is the direct squeezing transfer efficiency limited to approximately 50%, and can this be overcome with alternative protocols?
• RQ5 How do spectral response functions and noise correlations affect the performance of quantum memory and repeater operations?

Key findings

• Quasiperfect transfer of squeezed vacuum and EPR-entangled states between optical fields and atomic ensembles is theoretically achievable with high fidelity using EIT and Raman coupling.
• The storage and retrieval of quantum states in atomic ensembles are preserved with minimal decoherence, limited primarily by the long-lived ground state coherence decay rate γ₀.
• The maximum squeezing transfer efficiency from one atomic ensemble to another via the optical field is limited to approximately 54% (4/e² ≈ 0.54) due to spectral overlap of Lorentzian response functions.
• The optimal transfer time for maximum squeezing in the second ensemble occurs at t = 1/γε, with the variance of spin components reaching minimum at this point.
• The system supports transient entanglement between outgoing fields, with a lifetime governed by the phenomenological decay rate γ₀, which can be extended in cold atomic systems.
• Full quantum state transfer (e.g., for teleportation) requires a more advanced protocol, such as atomic teleportation, which combines the described mapping with entanglement swapping.