A novel qubit filter for photonic quantum computing

Shigeki Takeuchi

An optical-quantum-circuit entanglement filter can pass a pair of pho-tons with the desired polarization correlations. Photons are an important information-conveyance medium for enhanced computers and communications based on quantum mechanics. Filtering multiple photon states is a key capabili-ty in quantum-information science and technology, where one-quantum binary-digit (one-qubit) filters, or polarizers, have found wide application. Filtering based on the correlation or en-tanglement of photons requires multi-qubit filters with qubit-qubit interactions. We demonstrate an optical-entanglement filter that passes a pair of photons if they have the desired polarization correlations.1 The entangling capability of the filter was verified, distinguishing it from classical ones. Because our entanglement filter acts on photonic qubits, it is promising for quantum tech-

Yong‐Su Kim, Heedeuk Shin, Joonsuk Huh

Rafael Pereira da Silva

Jaromı́r Fiurášek, Robert Stárek, Michal Mičuda

We design optimal interferometric schemes for the implementation of two-qubit linear-optical quantum filters diagonal in the computational basis. The filtering is realized by the interference of the two photons encoding the qubits in a multiport linear-optical interferometer, followed by conditioning on presence of a single photon in each output port of the filter. The filter thus operates in the coincidence basis, similarly to many linear-optical unitary quantum gates. The implementation of a filter with linear optics may require an additional overhead in terms of a reduced overall success probability of the filtering and the optimal filters are those that maximize the overall success probability. We discuss in detail the case of symmetric real filters and extend our analysis also to asymmetric and complex filters.

Nicholas T. Bronn, Yanbing Liu, Jared Hertzberg +4 more

The ability to perform fast, high-fidelity readout of quantum bits (qubits) is essential for the goal of building a quantum computer. However, the parameters of a superconducting qubit device necessary to achieve this typically enhance qubit relaxation by spontaneous emission through the measurement channel. Here we design a broadband filter using impedance engineering to allow photons to leave the resonator at the cavity frequency but not at the qubit frequency. This broadband filter is implemented both in an on-chip and off-chip configuration.

R. B. Dalton, Geoff Gillett, Geoff J. Pryde +4 more