[Paper Review] Stopped and stationary light at the single-photon level inside a hollow-core fiber

Thorsten Peters, Ta-Pang Wang+3 more|arXiv (Cornell University)|Jun 13, 2019

Quantum optics and atomic interactions34 references4 citations

TL;DR

This paper demonstrates stopped and stationary light at the single-photon level using laser-cooled 87Rb atoms in a hollow-core photonic crystal fiber (HCPCF), achieving a signal-to-noise ratio of 59 through enhanced light-matter coupling and polarization filtering. By leveraging electromagnetically induced transparency (EIT) and mitigating birefringence effects, the platform enables efficient light storage and retrieval with narrowband pulses down to the single-photon level.

ABSTRACT

An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. We report on narrowband light storage and retrieval as well as stationary light, based on electromagnetically induced transparency, for weak coherent light pulses down to the single-photon level with a signal-to-noise ratio of 59. The experiments were carried out with laser-cooled atoms loaded into a hollow-core photonic crystal fiber to provide strong light-matter coupling, thereby demonstrating the prospects for future quantum networks of such a platform.

Motivation & Objective

• To enable quantum information processing with single-photon-level light-matter interaction in a scalable platform.
• To overcome background noise and birefringence limitations in waveguide-coupled atomic ensembles for high-fidelity quantum memory.
• To demonstrate light storage and retrieval (LSR) and stationary light pulses (SLPs) at the single-photon level using narrowband coherent pulses.
• To achieve high optical depth and strong coupling in a HCPCF while maintaining polarization filtering efficiency despite structural birefringence.
• To enable future quantum networks by combining high memory efficiency with low-power, low-noise operation using cold atoms in HCPCFs.

Proposed method

• Utilizes electromagnetically induced transparency (EIT) in a laser-cooled 87Rb atomic ensemble loaded into a hollow-core photonic crystal fiber (HCPCF).
• Employs a fine-structure transition with larger transition dipole moment to reduce required control beam power and minimize off-resonant absorption.
• Characterizes and compensates for linear birefringence in the HCPCF to maintain polarization states and enable effective background suppression via polarization filtering.
• Applies a rapidly modulated far-off-resonant trap (FORT) at 250 kHz to minimize ac Stark shifts during measurement windows while preserving atomic confinement.
• Uses a time-resolved detection scheme with single-photon counting modules (SPCMs) and digital oscilloscopes to record transmitted photons over 200 µs with 60 averaging cycles.
• Performs background subtraction using reference measurements without atoms to isolate signal from laser leakage and scattered photons.

Experimental results

Research questions

• RQ1 Can light storage and retrieval (LSR) and stationary light pulses (SLPs) be achieved at the single-photon level in a waveguide-coupled atomic system?
• RQ2 How can birefringence in hollow-core photonic crystal fibers be characterized and mitigated to preserve polarization filtering efficiency?
• RQ3 What is the achievable signal-to-noise ratio (SNR) for single-photon-level LSR and SLPs in a HCPCF-based platform?
• RQ4 Can high optical depth and strong light-matter coupling be maintained in a HCPCF while enabling low-power, low-noise EIT operation?
• RQ5 To what extent does rapid FORT modulation suppress ac Stark shifts without significant atomic loss during measurement windows?

Key findings

• The platform achieves a signal-to-noise ratio (SNR) of 59 for single-photon-level light storage and retrieval, enabling robust detection at the single-photon level.
• Background noise is reduced to 1.1 × 10⁴ photons per second with atoms and 0.7 × 10⁴ without, demonstrating effective suppression via polarization filtering despite birefringence.
• The system supports light storage and retrieval with a measured efficiency sufficient for quantum memory applications, enabled by high optical depth (d_opt ≲ 1000) in the HCPCF.
• The use of a fine-structure transition with larger transition dipole moment allows operation at lower control beam power, reducing off-resonant absorption and inhomogeneous shifts.
• Rapid FORT modulation at 250 kHz suppresses ac Stark shifts during 2.5 µs measurement windows, preserving atomic coherence and enabling up to 50 measurements per loading cycle.
• The experimental setup enables the generation of stationary light pulses (SLPs) and narrowband light storage with high fidelity, validating the platform’s potential for quantum networks.