We present recursive multiport schemes for implementing quantum Fourier transforms and the inversion step in Grover's algorithm on an integrated linear optics device. In particular, each scheme shows how to execute a quantum operation on
2d modes using a pair of circuits for the same operation on
d modes. The circuits operate on path-encoded qudits and realize
d-dimensional unitary transformations on these states using linear optical networks with
O(d2) optical elements. To evaluate the schemes against realistic errors, we ran simulations of proof-of-principle experiments using a simple fabrication model of silicon-based photonic integrated devices that employ directional couplers and thermo-optic modulators for beam splitters and phase shifters, respectively. We find that high-fidelity performance is achievable with our multiport circuits for 2-qubit and 3-qubit quantum Fourier transforms, and for quantum search on four-item and eight-item databases.
Summary form only given. Quantum optics experiments require ultimate control over the propagation of light in linear optical networks to realize programmable photon correlations [1]. Integrated optics provides a robust and low-loss platform for implementing such linear optical networks. However, to achieve ultimate control on the quantum state of light, it is necessary to program the network [2]. Tuning the network for controlled multiphoton correlations involves optimization algorithms which scale inefficiently with the network size and photon number. Therefore, it is challenging to scale up this approach to massively multichannel networks, which are required for large-scale implementations of quantum information processing and quantum communication.Here, we propose a novel method to achieve ultimate control on quantum light propagation through the adaptive control of phases at input channels of a massively multichannel network. We utilize an on-chip array of 3300 nearest-neighbor coupled silicon nitride waveguides as the network. We employ complex wavefront shaping methods, which enabled the creation of programmable linear optical networks in opaque scattering media [3,4], to realize a network with programmable quantum correlations in a fixed network [5]. Using a high brightness photon-pair source, we demonstrate programmable Hong-Ou-Mandel-like bunching or antibunching of photons in a fully tunable multichannel network as predicted by our theoretical work [6]. These results enable programmable photon correlations on fixed massively multichannel optical networks with the potential for large-scale implementation of quantum simulators and quantum logic gates. We will report on the progress of this project.