Work has focused on the development of a silicon quantum photonic technology platform and components [1], aimed toward the project goal of achieving a scalable approach to quantum information technologies through silicon quantum photonic integration.
Outlined below are a selection of achievements across the projects’ five major objectives:
1) Scaling quantum complexity: Increasing the number of photons and the number of modes within a quantum system are two ways in which the complexity of quantum photonic circuits can be scaled. To investigate large-mode systems we developed a complex quantum photonic circuit capable of generating, manipulating and analysing multi-dimensional entangled states. The circuit implemented comprises 16 integrated photon sources, and was successfully used in demonstrating 15x15 dimensional entanglement of a two photon state [2, 3]. To investigate large photon number systems, we created a silicon quantum photonic circuit capable of the on-chip generation and algorithmic processing of quantum states of light with up to eight photons [4].
2) Large-scale programmable quantum circuits: Programmable quantum circuits allow a single chip to perform many different functions. We realised a quantum photonic circuit able to implement any two-qubit unitary quantum operation [5] and was programmed to implement 98 different two-qubit quantum logic gates (including CNOT, CZ, CH, SWAP, iSWAP and SWAP). Additionally, we realised a silicon chip that programmatically generates four-photon graphs states – a key resource state in measurement-based quantum computing [5].
3) Integrated quantum technology platform: The project has made major strides towards a fully integrated technology platform, with the successful integration of multiple photon-sources within single integrated circuits [2]. Ring-resonator-based sources were integrated within reconfigurable circuits to demonstrate qubit entanglement and indistinguishable photon generation [7]. Cryogenic-compatible optical modulators have also been developed to enable future integration with cryogenic superconducting single photon detectors [8].
4) Ultra-compact and practical quantum communications devices: Integrated photonics provides a stable, compact, miniaturised and robust platform to implement quantum communications systems. Through this project we demonstrated the world’s first chip-to-chip quantum communications system, realising integrated quantum communications devices in both the InP [9] and Silicon [10] material platforms.
5) Quantum simulation and computation: Entanglement is a fundamental property of quantum mechanics and is a primary resource in quantum information systems. We implemented a device which can generate, manipulate, and analyse two-qubit entangled states and manipulate their entanglement through a switchable controlled-Z gate operates [11]. Programmable quantum circuits were developed to investigate quantum computing applications in quantum simulation [12] and quantum Hamiltonian learning [13], where we successfully realised a quantum simulator that could learn the physics of another quantum system. Moving beyond a single isolated system has been achieved through the demonstration of chip-to-chip quantum teleportation [14] – an important requirement for future distributed quantum computing systems.
[1] Silverstone et al, Silicon Quantum Photonics, IEEE J. Sel. Top. Quantum Electron., 22, 1–13, 2016
[2] Wang et al, Multidimensional quantum entanglement with large-scale integrated optics, Science, eaar7053, 2018
[3] Faruque et al, On-chip quantum interference with heralded photons from two independent micro-ring resonator sources in silicon photonics, Opt. Express, 26, 20379–20395, 2018
[4] Paesani et al, Generation and sampling of quantum states of light in a silicon chip, Nat Phys, 273, 1, 2019
[5] Adcock et al, Programmable four-photon graph states on a silicon chip, Nat Comms, 10, 1, 1–6, 2019
[6] Qiang et al, Large-scale silicon quantum photonics implementing arbitrary two-qubit processing, Nature photonics, 12, 534–539, 2018
[7] Silverstone et al, Qubit entanglement between ring-resonator photon-pair sources on a silicon chip, Nat Comms, 6, 7948, 2015
[8] Eltes et al. An integrated cryogenic optical modulator, Submitted 2019 arxiv.org/abs/1904.10902
[9] Sibson et al, Chip-based quantum key distribution, Nat Comms, 8, 13984, 2017
[10] Sibson et al, Integrated silicon photonics for high-speed quantum key distribution, Optica, 4, 172–177, 2017
[11] Santagati et al, Silicon photonic processor of two-qubit entangling quantum logic, J. Opt., 19, 114006, 2017
[12] Santagati et al, Witnessing eigenstates for quantum simulation of Hamiltonian spectra, Science Advances, 4, 1, eaap9646, 2018
[13] Wang et al, Experimental quantum Hamiltonian learning, Nat Phys, 6, 031007, 2017
[14] Llewellyn et al, Chip-to-chip quantum teleportation and multi-photon entanglement in silicon, Submitted Nov 2019 arXiv:1911.07839
