Publications by

Testing multi-photon interference on a silicon chip

Optics Express Optical Society of America 27 (2019) 35646-35658

B Bell, GS Thekkadath, R Ge, X Cai, IA Walmsley

Shape-preserving and unidirectional frequency conversion using four-wave mixing Bragg scattering

Optics Express Optical Society of America 26 (2018) 17145-17157

JB Christensen, JG Koefoed, B Bell, CJ McKinstries, K Rottwitt

In this work, we investigate the properties of four-wave mixing Bragg scattering driven by orthogonally polarized pumps in a birefringent waveguide. This configuration enables a large signal conversion bandwidth, and allows strongly unidirectional frequency conversion as undesired Bragg-scattering processes are suppressed by waveguide birefringence. Moreover, we show that this form of Bragg scattering preserves the (arbitrary) signal pulse shape, even when driven by pulsed pumps.

Multiphoton interference in the spectral domain by direct heralding of frequency superposition states

Physical Review Letters American Physical Society 121 (2018) 033601-

B Bell, BJ Eggleton

Multi-photon interference is central to photonic quantum information processing and quantum simulation, usually requiring multiple sources of non-classical light followed by a unitary transformation on their modes. Here, we observe interference in the four-photon events generated by a single silicon waveguide, where the different modes are six frequency channels. Rather than requiring a unitary transformation, the frequency correlations of the source are configured such that photons are generated in superposition states across multiple channels, and interference effects can be seen without further manipulation. The frequency correlations of the source also means that it is effectively acting as multiple pair photon sources, generating photons in different spectral modes, which interfere with each other in a non-trivial manner. This suggests joint spectral engineering is a tool for controlling complex quantum photonic states without the difficulty of implementing spatially separate sources or a large unitary interferometer, which could have practical benefits in various applications of multi-photon interference.

Integrated silicon nitride time-bin entanglement circuits

Optics Letters Optical Society of America 43 (2018) 3469-3472

X Zhang, B Bell, A Mahendra, C Xiong, PHW Leong, BJ Eggleton

Time-bin entangled photons allow robust entanglement distribution over quantum networks. Integrated photonic circuits positioned at the nodes of a quantum network can perform the important functions of generating highly entangled photons and precisely manipulating their quantum state. In this Letter, we demonstrate time-bin entangled photon generation, noise suppression, wavelength division, and entanglement analysis on a single photonic chip utilizing low-loss double-stripe silicon nitride waveguide structures. Quantum state tomography results show 91±0.7% fidelity compared with the ideal state, indicating that highly entangled photons are generated and analyzed. This work represents a crucial step toward practical quantum networks.

Topological protection of biphoton states

Science American Association for the Advancement of Science 362 (2018) 568-571

A Blanco Redondo, B Bell, D Oren, BJ Eggleton, M Segev

The robust generation and propagation of multiphoton quantum states are crucial for applications in quantum information, computing, and communications. Although photons are intrinsically well isolated from the thermal environment, scaling to large quantum optical devices is still limited by scattering loss and other errors arising from random fabrication imperfections. The recent discoveries regarding topological phases have introduced avenues to construct quantum systems that are protected against scattering and imperfections. We experimentally demonstrate topological protection of biphoton states, the building block for quantum information systems. We provide clear evidence of the robustness of the spatial features and the propagation constant of biphoton states generated within a nanophotonics lattice with nontrivial topology and propose a concrete path to build robust entangled states for quantum gates.