## Abstract

Recently there has been a worldwide effort to produce scalable qubit implementations for quantum information protocols, including quantum key distribution, quantum metrology and quantum computing---technologies which have the power to revolutionise their respective fields. Silicon photonics is in a prime position to provide the physical, photonic implementations of these technologies due to it's high-yield, high-performance and inherently scalable CMOS manufacturing infrastructure.

The on-chip production of more than one uncorrelated photon pair (more than two photons) has remained a technological challenge. Here, we seek to overcome this using careful quantum photonic design, and state-of-the-art Silicon photonics technology. Our four-photon device expands the capabilities of integrated quantum photonics to fully entangled four photons, specifically the four photon graph states.

In the graph state formalism, each vertex corresponds to a qubit, and each edge corresponds to a controlled-phase gate (an entangling operation) performed between the qubits it links. It has been shown that these states are very powerful---simple measurement strategies on certain graph states provide universal quantum computing. Interestingly, certain classes of graph states are equivalent under single-qubit transformations. These are the global entanglement classes. Our device uses both a reconfigurable entangling gate and local transformations to fully explore the space of 4 qubit graph states.

The device employs four ring resonator sources, on-chip spectral demultiplexing, a reconfigurable entangling gate, and single-qubit transformations for each qubit. Using these capabilities, we can verify our entangled quantum states using entanglement witnesses, local tomography, and by running toy measurement-based quantum computations.

These devices will be both the largest and most diverse integrated photonic quantum state generators produced to date. A vital demonstration of this work is high-quality quantum interference between spontaneous four-wave mixing photon-pair sources on the same chip.

These ideas and proof-of-concept demonstrations point to large scale quantum technology, built using today's technologies.

The on-chip production of more than one uncorrelated photon pair (more than two photons) has remained a technological challenge. Here, we seek to overcome this using careful quantum photonic design, and state-of-the-art Silicon photonics technology. Our four-photon device expands the capabilities of integrated quantum photonics to fully entangled four photons, specifically the four photon graph states.

In the graph state formalism, each vertex corresponds to a qubit, and each edge corresponds to a controlled-phase gate (an entangling operation) performed between the qubits it links. It has been shown that these states are very powerful---simple measurement strategies on certain graph states provide universal quantum computing. Interestingly, certain classes of graph states are equivalent under single-qubit transformations. These are the global entanglement classes. Our device uses both a reconfigurable entangling gate and local transformations to fully explore the space of 4 qubit graph states.

The device employs four ring resonator sources, on-chip spectral demultiplexing, a reconfigurable entangling gate, and single-qubit transformations for each qubit. Using these capabilities, we can verify our entangled quantum states using entanglement witnesses, local tomography, and by running toy measurement-based quantum computations.

These devices will be both the largest and most diverse integrated photonic quantum state generators produced to date. A vital demonstration of this work is high-quality quantum interference between spontaneous four-wave mixing photon-pair sources on the same chip.

These ideas and proof-of-concept demonstrations point to large scale quantum technology, built using today's technologies.

Original language | English |
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Publication status | Published - 2016 |

Event | Photon 16 - University of Leeds, Leeds, United Kingdom Duration: 5 Sep 2016 → 8 Sep 2016 |

### Conference

Conference | Photon 16 |
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Country | United Kingdom |

City | Leeds |

Period | 5/09/16 → 8/09/16 |