title: Linear optical quantum computing in a single spatial mode.
abstract: We present a scheme for linear optical quantum computing using time-bin-encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled-phase (cphase) gates, providing a sufficient set of operations for universal quantum computing with the Knill-Laflamme-Milburn [Nature (London) 409, 46 (2001)] scheme. Our protocol is suited to currently available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84±0.07.
authors.affiliation: Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Humphreys
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Metcalf
authors.forename: Justin B
authors.initials: JB
authors.lastname: Spring
authors.forename: Merritt
authors.initials: M
authors.lastname: Moore
authors.forename: Xian-Min
authors.initials: XM
authors.lastname: Jin
authors.forename: Marco
authors.initials: M
authors.lastname: Barbieri
authors.forename: W Steven
authors.initials: WS
authors.lastname: Kolthammer
authors.forename: Ian A
authors.initials: IA
authors.lastname: Walmsley