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Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR)

Single-photon buffer at a telecommunication wavelength using a fiber-optic switch

Akiko Tada, Naoto Namekata, Shuichiro Inoue

Published Jul 1, 2017• 0 citations
Publisher

Abstract

We demonstrated an efficient fiber-optic single-photon buffer (SPB) at 1550 nm. The SPB can control and give discrete time delays to a single-photon. Moreover the SPB is passively polarization-stable, and consequently the polarization-based quantum state of light can be maintained. The insertion loss of the SPB is as low as 2.98 dB, which indicates that it can be used for enhancement of efficiencies of heralding single-photon sources and multi-photon interference experiments.

DOI
10.1109/cleopr.2017.8118925

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We demonstrated an efficient fiber-optic single-photon buffer (SPB) at 1550 nm. The SPB can control and give discrete time delays to a single-photon. Moreover the SPB is passively polarization-stable, and consequently the polarization-based quantum state of light can be maintained. The insertion loss of the SPB is as low as 2.98 dB, which indicates that it can be used for enhancement of efficiencies of heralding single-photon sources and multi-photon interference experiments.
Abstract We report a fiber loop quantum buffer based on a low-loss 2 × 2 switch and a unit delay made of a fiber delay line. We characterize the device by using a two-photon polarization entangled state in which one photon of the entangled photon pair is stored and retrieved at a repetition rate up to 78 kHz. The device, which enables integer multiples of a unit delay, can store the qubit state in a unit of fiber delay line up to 5.4 km and the number of loop round-trips up to 3. Furthermore, we configure the device with other active elements to realize integer multiplier and divider of a unit delay of a qubit. The quantum state tomography is performed on the retrieved photon and its entangled photon. We obtain a state fidelity > 94 % with a maximum storage time of 52 μs with an insertion loss of 5.56 dB. To further characterize the storing and retrieving processes of the device, we perform entanglement-assisted quantum process tomography on the buffered qubit state. The process fidelity of the device is > 0.98. Our result implies that the device preserves the superposition and entanglement of a qubit state from a two-photon polarization-entangled state. This is a significant step towards facilitating applications in optical asynchronous transfer mode based quantum networks.
A crucial component of photonic quantum information processing platforms is the ability to modulate, route, convert, and switch quantum states of light noiselessly with low insertion loss. For instance, a high-speed, low-loss optical switch is crucial for scaling quantum photonic systems that rely on measurement-based feed-forward approaches. Such a device will also ideally be capable of operating on photon-number states, which can act as non-Gaussian resources. Here, we demonstrate ultrafast all-optical switching of heralded photon-number states, of up to 6 photons, using the optical Kerr effect in a single-mode fiber. A local birefringence is created by a high-intensity pump pulse at a center wavelength of 1030 nm which overlaps temporally with the 1550 nm photons in the fiber. A switching efficiency of $>$99 % is reached with a resolution of 2.3 ps, an insertion loss of 2.27±0.082.27\pm0.082.27±0.08 dB, and a signal-to-noise ratio of 32,000.
Single-photon sources based on spontaneous photon-pair generation have enabled pioneering experiments in quantum physics. However, next-generation photonic quantum technologies require higher generation probabilities of photons in well-controlled pure states capable of high-visibility interference. We have harnessed bespoke fiber technology to develop virtually alignment-free sources that deliver high-purity heralded single photons in telecoms single-mode fiber. The resulting access to low-loss optical delay enabled us to actively route the heralded output from two almost identical sources to enhance the delivery probability of single photons relative to one individual source. Our results indicate how the scale of photonic quantum technologies might be increased via guided-wave multiplexing of high-purity photons.
Quasi-deterministic single-photon generation is a key requirement for many photonic quantum technologies. Photon sources based on spontaneous parametric down-conversion (SPDC) are widely used for producing high-quality photons; however, the probabilistic nature of the process limits the generation of synchronized multi-photon states. Here, we demonstrate temporal synchronization of multiple photon-generation events using a free-space-fiber hybrid delay line with feed-forward control, enabling fast and efficient switching and scalable operation. Narrow-band, telecom-wavelength photons compatible for fiber transmission are heralded from a monolithic cavity SPDC source and synchronized across 20 time bins. This yields a sixfold enhancement in synchronized rates and enables multi-photon synchronization, with only a marginal increase of higher-order photon-number contributions.
Dynamically routing single photons without disturbing their quantum state is an essential capability for photonic quantum information technology. Here, we experimentally demonstrate a heralded single-photon switch that combines low loss, strict polarization independence, and high process fidelity in a simple architecture based on a free-space Sagnac interferometer incorporating a single Pockels cell. The routing of the photon between two spatial output modes is governed solely by the phase modulation applied to the Pockels cell, and is therefore independent of the input polarization state, while the Sagnac geometry provides passive interferometric stability without active phase locking. Operating at the telecom wavelength of 1550 nm, the switch exhibits an insertion loss of approximately 0.4 dB and an average extinction ratio of 19.1 dB. Quantum process tomography yields process fidelities of 0.985 and 0.979 with respect to the ideal identity operation for the two output modes, demonstrating that the polarization information encoded in the single photons is preserved through the switch. These features make the device a practical building block for fundamental quantum optics experiments, photonic quantum information processing, and quantum networks at telecom wavelengths.