[Paper Review] Characterizing micro-macro transitions with an atomic-vapor-based linear optical amplifier

Zhifan Zhou, Ulrich Vogl+5 more|arXiv (Cornell University)|May 24, 2016

Quantum optics and atomic interactions40 references3 citations

TL;DR

This paper demonstrates a high-gain, atomic-vapor-based linear optical amplifier using four-wave mixing in hot rubidium vapor to characterize micro-macro transitions. It achieves a 10⁷ optical gain, enabling photon-number-resolving detection of single-photon-level inputs via conventional detectors, with group-velocity delay scaling as 1/√N, where N is the average input photon number. The probe and conjugate modes exhibit distinct scaling coefficients, providing a sensitive parameter to characterize quantum-to-classical transitions.

ABSTRACT

Fundamentally, the dynamics of micro-macro transitions is instrumental to understanding the process of quantum-to-classical transitions; technologically, it can also facilitate the detection of the microscopic signals in quantum experiments via convenient detectors. Here, we demonstrate a scheme to characterize micro-macro transitions based on a four-wave mixing linear optical amplification process in a hot rubidium vapor. The linear optical amplifier provides a large optical gain of $10^7$ for injected single-photon-level pulses, enabling photon-number-resolving detection by average via non-single-photon counting detectors with a large dynamic range. The scheme exhibits strong dispersion which is sensitive to the input's change at the single-photon level, resulting in the group-velocity delay time scaling with $1/\sqrt{N}$, where $N$ is the average input photon number. The output probe and conjugate modes have different coefficients of this $1/\sqrt{N}$ scaling, indicating the coefficient can serve as an efficient parameter to characterize the specified micro-macro transitions. The demonstrated results are generally applicable for quantum detection and optical signal processing in light-atom interfaces. Furthermore, the present system is suitable for the study of relevant time-resolved dynamics of the quantum-to-classical transitions.

Motivation & Objective

• To develop a method for experimentally probing micro-macro transitions in quantum-to-classical dynamics.
• To overcome limitations in existing systems where micro-level input changes are not resolved due to inhomogeneous broadening.
• To enable photon-number-resolving detection of single-photon-level signals using non-single-photon-counting detectors with large dynamic range.
• To characterize the temporal dynamics of micro-macro transitions through dispersion-sensitive group-velocity delay scaling.
• To identify a scalable, quantifiable parameter—scaling coefficient of delay time with 1/√N—for distinguishing different micro-macro transition behaviors.

Proposed method

• Utilizes four-wave mixing in a double-lambda configuration within a hot rubidium-85 vapor to achieve linear optical amplification.
• Employs a strong, non-depleted pump beam to maintain linearity and suppress spontaneous emission and resonant absorption.
• Exploits electromagnetically induced transparency-like quantum interference to enhance nonlinearity and induce strong dispersion.
• Measures group-velocity delay time as a function of average input photon number N to observe 1/√N scaling behavior.
• Uses non-single-photon-counting detectors to measure amplified output pulses, enabling photon-number resolution over a large dynamic range.
• Analyzes both probe and conjugate output modes to compare their distinct 1/√N scaling coefficients, which reflect differential absorption and dispersion.

Experimental results

Research questions

• RQ1 How can micro-macro transitions be experimentally resolved with sensitivity to single-photon-level input changes?
• RQ2 What is the scaling behavior of group-velocity delay time with respect to average input photon number N in a highly dispersive atomic medium?
• RQ3 Can the scaling coefficient of the 1/√N delay dependence serve as a distinguishable parameter for characterizing different micro-macro transition pathways?
• RQ4 How does the linear optical amplifier enable photon-number-resolving detection using conventional, non-single-photon-counting detectors?
• RQ5 What is the role of differential absorption in probe and conjugate beams in modulating the delay-time scaling coefficient?

Key findings

• The system achieves an optical gain of 10⁷ for single-photon-level input pulses, enabling macroscopic detection via standard detectors.
• The group-velocity delay time scales as 1/√N over a dynamic range from ~1 to ~800 average input photons, with quantitative agreement to theoretical predictions.
• The probe mode exhibits a 1/√N scaling coefficient of 0.729 ± 0.292 × 10⁵ GHz/√pW, while the conjugate mode has 2.154 ± 0.33 × 10⁵ GHz/√pW, indicating different dispersion responses.
• Pulse shapes in the conjugate mode show minimal distortion at low input powers, with peak amplitudes following the predicted 1/√N dependence.
• The observed delay-time scaling is robust and measurable over a large dynamic range, confirming the system’s suitability for time-resolved quantum dynamics studies.
• The differential scaling coefficients between probe and conjugate beams provide a sensitive, quantifiable parameter for characterizing specific micro-macro transition processes.