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Optics Express

Spectral characterization of single photon sources with ultra-high resolution, accuracy and sensitivity

Lijun Ma, Oliver Slattery, Xiao Hong Tang

Published Nov 7, 2017• 3 citations
Publisher

Abstract

In future quantum communication systems, single photons, as the information carriers, are required to possess very narrow linewidths and accurate wavelengths for an efficient interaction with quantum memories. Spectral characterization of such single photon sources is necessary and must be performed with very high spectral resolution, wavelength accuracy and detection sensitivity. In this paper, we propose a method to precisely characterize spectral properties of narrow-linewidth single-photon sources using an atomic vapor cell based on electromagnetically-induced transparency (EIT). By using an atomic cesium vapor cell, we have experimentally demonstrated a spectral resolution of better than 150 kHz, an absolute wavelength accuracy of within 50 kHz and an exceptional detection sensitivity suitable for optical signals as weak as −117 dBm.

DOI
10.1364/oe.25.028898

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•Jan 1, 2015•0 citations
In future quantum communication systems, single photons, as the information carriers, are required to possess very narrow linewidths and accurate wavelengths for an efficient interaction with quantum memories. Spectral characterization of such single photon sources is necessary and must be performed with very high spectral resolution, wavelength accuracy and detection sensitivity. In this paper, we propose a method to precisely characterize spectral properties of narrow-linewidth single-photon sources using an atomic vapor cell based on electromagnetically-induced transparency (EIT). By using an atomic cesium vapor cell, we have experimentally demonstrated a spectral resolution of better than 150 kHz, an absolute wavelength accuracy of within 50 kHz and an exceptional detection sensitivity suitable for optical signals as weak as −117 dBm.
In future quantum communication systems, single photons will be required to possess very narrow linewidths and accurate wavelengths for efficient interaction with quantum memories. Spectral characterization of such single photon sources is necessary and must be performed with very high spectral resolution, wavelength accuracy and detection sensitivity. We propose a method to precisely characterize the spectral properties of narrow-linewidth single-photon sources using an atomic vapor cell based on electromagnetically-induced transparency. We have experimentally demonstrated a spectral resolution of better than 150 kHz, an absolute wavelength accuracy of within 50 kHz and an exceptional detection sensitivity suitable for optical signals as weak as -117 dBm.
Quantum memories play a pivotal role in establishing long-distance communication by entanglement swapping operations within quantum repeater nodes. Constructing such a quantum memory involves Electromagnetically Induced Transparency (EIT) within atomic vapors at room temperatures to store highly attenuated coherent light pulses down to the level of single photons. The photons may be generated from quantum nodes containing stationary quantum systems, such as atoms or semiconductor quantum dots (QDs). QDs serve as a potent source of quantum light, furnishing bright, precisely timed single photons of exceptional purity. While previous endeavors have demonstrated the integration of QDs with atomic vapors through techniques like “slow light,” the development of a dedicated quantum memory for QDs remains unmatched. In our study, we introduce an EIT quantum memory hosted within warm cesium vapor. Our approach exhibits a good efficiency in storing faint coherent light pulses at the single photon level. Moreover, the measured bandwidth of around 200 MHz approaches the Fourier-limited emission characteristics of QDs. We present initial efforts to match the emission from QDs with our quantum memory and discuss application scenarios of room temperature EIT quantum memories.
Quantum memories can substantially increase the efficiency of long-distance communications by synchronizing entanglement swapping operations in quantum repeater nodes. To build a quantum memory, electromagnetically induced transparency (EIT) in atomic vapors can be exploited to coherently store light pulses even at room temperatures. As a quantum source of light, semiconductor quantum dots (QD) offer bright on-demand single photons with high purity.4 Interfacing QDs with atomic vapors has been shown by “slow light” but a quantum memory for QDs is yet to be demonstrated. In this work, we develop an EIT quantum memory hosted in warm cesium vapor. Storage of faint coherent light pulses on the single photon level shows high storage efficiency. A measured bandwidth in the order of 200 MHz makes the memory compatible with the Fourier-limited emission of QDs embedded in micropillar cavities. We show the first attempts to interface the emission from a QD-micropillar with our quantum memory by finetuning the emission wavelength of the emitters to one of the hyperfine transitions in Cs, where the EIT memory takes place. This work sets the base for a hybrid quantum memory based on atomic ensembles for an on-demand semiconductor single-photon source.
Rydberg-atom electrometry is a core technique in the development of highly sensitive quantum electric-field sensors. Its sensitivity based on atom-photon interaction is typically limited by photon shot-noise (PSN) and spectral broadenings. Here, we experimentally demonstrate a near PSN-limited Rydberg electrometry from a 85Rb atomic vapor cell. By engineering atomic coherence through control of residual magnetic fields and laser frequency noise, we achieve the Rydberg electromagnetically induced transparency (EIT) with the narrow linewidth of 1.6 MHz, yielding an enhanced spectral slope for high-sensitivity Rydberg-EIT electrometry. Under optimized superheterodyne detection conditions, we obtain an electric-field sensitivity of 12.5(8) nV cm^-1 Hz^-1/2 at 37 GHz, in close agreement with the calculated PSN limit. These results provide direct experimental evidence of the high-sensitive quantum electrometry and establish a practical route toward quantum-noise-limited Rydberg electrometry.
A single-photon source with narrow bandwidth, high purity, and large brightness can efficiently interact with material qubits strongly coupled to an optical microcavity for quantum information processing. Here, we experimentally demonstrate a degenerate doubly resonant single-photon source at 852 nm by the cavity-enhanced spontaneous parametric down-conversion process with a 100% duty cycle of generation. The single photon source possesses both high purity with a second-order correlation g (2) (0) = 0.021 and narrow linewidth with Δνsp = (800 ± 13) kHz. The single-photon source is compatible with the cesium atom D2 line and can be used for cesium-based quantum information processing.
This thesis describes work on single-photon pair creation, entanglement and entanglement measurement; single-photon spectral narrowing for atomic interaction; and single-photon detection and spectral analysis. The systems developed exploit the interactions of light beams in non-linear crystal materials. Greatly non-degenerate time-bin entangled photon pair sources are implemented based on the quantum process of spontaneous-parametric-down-conversion. The non-degenerate wavelengths correspond to an atomic transition (895 nm) and a telecommunications band (1310 nm). Interference-fringe-visibilities of over 78% are achieved, verifying entanglement. An efficient and low-noise single-photon up-conversion detector based on sum-frequency-generation is implemented. Photons at 1310 nm are converted to the visible region and efficiently detected using a visible single-photon detector. An overall detection efficiency of over 32% is achieved with a dark-count noise rate of 2500 s-1. The detector is further developed to achieve an inter-symbol-interference free detection rate at twice the limit of the type of visible detector used. The detector is adapted into an up-conversion spectrometer for wavelengths near 1310 nm. A sensitivity of -126 dBm is achieved, corresponding to photon fluxes of approximately 500 s-1. The up-conversion spectrometer is further adapted for correlated biphoton spectroscopy by incorporating a frequency entangled and time correlated source. In this scheme, the spectral function near 895 nm of a remote object can be reproduced by locally measuring the 1310 nm with the up-conversion spectrometer and monitoring the coincidence detection rates. To achieve linewidths feasible for atomic interaction, a very narrow linewidth non-degenerate single-photon pair source is implemented based on spontaneous-parametric-down-conversion embedded in a singly-resonant cavity which is locked to and resonating at the frequency corresponding to a target atomic transition. Linewidths as narrow as 28 MHz are achieved. The brightness of the source within the modes is increased by two-orders compared to the single-pass implementations.