Compensation-free broadband entangled photon pair sources

Single-pass generation of widely-tunable frequency-domain entangled photon pairs

We demonstrate a technique that generates frequency-entangled photon pairs with strong polarization correlation by using a single-period nonlinear crystal and single pass configuration. The technique is based on the simultaneous occurrence of two spontaneous parametric down-conversion processes satisfying independent type-II collinear quasi-phase matching conditions in periodically poled stoichiometric lithium tantalate. The generated photon pairs exhibit non-degenerate Hong-Ou-Mandel interference, indicating the presence of quantum entanglement in the frequency domain. This method provides a light source capable of wide-range quantum sensing and quantum imaging or high-dimensional quantum processing.

Entangled-Based Quantum Wavelength-Division-Multiplexing and Multiple-Access Networks

This paper investigates the mathematical model of the quantum wavelength-division-multiplexing (WDM) network based on the entanglement distribution with the least required wavelengths and passive devices. By adequately utilizing wavelength multiplexers, demultiplexers, and star couplers, N wavelengths are enough to distribute the entanglement among each pair of N users. Moreover, the number of devices employed is reduced by substituting a waveguide grating router for multiplexers and demultiplexers. Furthermore, this study examines implementing the BBM92 quantum key distribution in an entangled-based quantum WDM network. The proposed scheme in this paper may be applied to potential applications such as teleportation in entangled-based quantum WDM networks.

Broadband polarization-entangled source for C+L-band flex-grid quantum networks

The rising demand for transmission capacity in optical networks has motivated steady interest in expansion beyond the standard C-band (1530-1565 nm) into the adjacent L-band (1565-1625 nm) for an approximate doubling of capacity in a single stroke. However, in the context of quantum networking, the L-band has yet to be fully leveraged with the suite of advanced tools for characterization and management available from classical lightwave communications. In this work, we demonstrate an ultrabroadband two-photon source integrating both C- and L-band wavelength-selective switches for complete control of spectral routing and allocation across 7.5 THz in a single setup. Polarization state tomography of all 150 pairs of 25-GHz-wide channels reveals an average fidelity of 0.98 and total distillable entanglement greater than 181 kebits/s. This source is explicitly designed for flex-grid optical networks and can facilitate optimal utilization of entanglement resources across the full C+L-band.

Spectrally pure photons generated in a quasi-phase matched xenon-filled hollow-core photonic crystal fiber

Spectrally pure photons heralded from unentangled photon pair sources are crucial for any quantum optical system reliant on the multiplexing of heralded photons from independent sources. Generation of unentangled photon pairs in gas-filled hollow-core photonic crystal fibers specifically remains an attractive architecture for integration into quantum-optical fiber networks. The dispersion design offered by selection of fiber microstructures and gas pressure allows considerable control over the group-velocity profile which dictates the wavelengths of photon pairs that can be generated without spectral entanglement. Here, we expand on this design flexibility, which has previously been implemented for four-wave mixing, by modeling the use of a static, periodically poled electric field to achieve an effective quasi-phase-matched three-wave mixing nonlinearity that creates spontaneous parametric downconversion. Electric-field-induced quasi-phase-matched spontaneous parametric downconversion enables control of phase matching conditions that is independent of the group velocity, allowing phase matching at arbitrary wavelengths without affecting the entanglement of photons at those wavelengths. This decoupling of entanglement engineering and phase matching facilitates spectrally pure photon pair generation with efficiency and wavelength-tunability that is otherwise unprecedented.

Entangled photon-pair sources based on three-wave mixing in bulk crystals

Entangled photon pairs are a critical resource in quantum communication protocols ranging from quantum key distribution to teleportation. The current workhorse technique for producing photon pairs is via spontaneous parametric down conversion (SPDC) in bulk nonlinear crystals. The increased prominence of quantum networks has led to a growing interest in deployable high performance entangled photon-pair sources. This manuscript provides a review of the state-of-the-art bulk-optics-based SPDC sources with continuous wave pump and discusses some of the main considerations when building for deployment.

Broadband fiber-based entangled photon-pair source at telecom O-band

In this Letter, we report a polarization-entangled photon-pair source based on type-II spontaneous parametric downconversion at telecom O-band in periodically poled silica fiber (PPSF). The photon-pair source exhibits more than 130 nm (∼24THz) emission bandwidth centered at 1306.6 nm. The broad emission spectrum results in a short biphoton correlation time, and we experimentally demonstrate a Hong-Ou-Mandel interference dip with a full width of 26.6 fs at half-maximum. Owing to the low birefringence of the PPSF, the biphotons generated from type-II SPDC are polarization-entangled over the entire emission bandwidth, with a measured fidelity to a maximally entangled state greater than 95.4%. The biphoton source provides the broadest bandwidth entangled biphotons at O-band to our knowledge.

Dispersion measurement assisted by a stimulated parametric process

Dispersion plays a major role in the behavior of light inside photonic devices. Current state-of-the-art dispersion measurement techniques utilize linear interferometers that can be applied to devices with small dispersion-length products. However, linear interferometry often requires beam alignment and phase stabilization. Recently, common-path nonlinear interferometers in the spontaneous regime have been used to demonstrate alignment-free and phase-stable dispersion measurements. However, they require single-photon detectors, resulting in high system cost and long integration times. We overcome these issues by utilizing a nonlinear interferometer in the stimulated regime and demonstrate the ability to measure the dispersion of a device with a dispersion-length product as small as 0.009 ps/nm at a precision of 0.0002 ps/nm. Moreover, this regime allows us to measure dispersion with shorter integration times (in comparison to the spontaneous regime) and conventional optical components and detectors.

High-performance source of spectrally pure, polarization entangled photon pairs based on hybrid integrated-bulk optics

Entangled photon pair sources based on bulk optics are approaching optimal design and implementation, with high state fidelities, spectral purities and heralding efficiencies, but generally low brightness. Integrated entanglement sources, while providing higher brightness and low-power operation, often sacrifice performance in output state quality and coupling efficiency. Here we present a polarization-entangled pair source based on a hybrid approach of waveguiding and bulk optics, addressing every metric simultaneously. We show 96 % fidelity to the singlet state, 82 % Hong-Ou-Mandel interference visibility, 43 % average Klyshko efficiency, and a high brightness of 2.9 × 10⁶ pairs/(mode·s·mW), while requiring only microwatts of pump power.