Remote state preparation (RSP) is the act of preparing a quantum state at a remote location without actually [...]]]> Our paper, Derivation and experimental test of fidelity benchmarks for remote preparation of arbitrary qubit states, was published in Physical Review A.  This work was done in collaboration with Norbert Lütkenhaus at IQC.

Remote state preparation (RSP) is the act of preparing a quantum state at a remote location without actually transmitting the state itself. Using at most two classical bits and a single shared maximally entangled state, one can in theory remotely prepare any qubit state with certainty and with perfect fidelity. However, in any experimental implementation the average fidelity between the target and output states cannot be perfect. In order for an RSP experiment to demonstrate genuine quantum advantages, it must surpass the optimal threshold of a comparable classical protocol. Here we study the fidelity achievable by RSP protocols lacking shared entanglement and determine the optimal value for the average fidelity in several different cases. We implement an experimental scheme for deterministic remote preparation of arbitrary photon polarization qubits, preparing 178 different pure and mixed qubit states with an average fidelity of 0.995. Our experimentally achieved average fidelities surpass our derived classical thresholds whenever the classical protocol does not trivially allow for perfect RSP.

Classical thresholds and their violation in our experiment

We introduce and implement a technique to extend the quantum computational power of cluster states by replacing [...]]]> Our article, Cluster-State Quantum Computing Enhanced by High-Fidelity Generalized Measurements, was published in Physical Review Letters.  This work was done with Terry Rudolph at Imperial College and Gregor Weihs at the University of Innsbruck.

We introduce and implement a technique to extend the quantum computational power of cluster states by replacing some projective measurements with generalized quantum measurements (POVMs). As an experimental demonstration we fully realize an arbitrary three-qubit cluster computation by implementing a tunable linear-optical POVM, as well as fast active feedforward, on a two-qubit photonic cluster state. Over 206 different computations, the average output fidelity is 0.9832±0.0002; furthermore the error contribution from our POVM device and feedforward is only of O(), less than some recent thresholds for fault-tolerant cluster computing.