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Designing Optimal States and Transformations for Quantum Optical Communication and Metrology

Dmitry Uskov, Tulane/LSU

(Session 9 : Saturday from 4:30-5:00)

Abstract. Entangled states of light are in great demand in quantum technology today. Photonic quantum communication, information processing, and metrology are all based on exploiting special properties of non-classical multipath entangled states. Generation of such states and quantum operations on them require effective photon-photon interaction which may be produced using ancilla modes and projective measurements. We will report on our study of optimal implementations of optical measurement-assisted transformations of non-classical photonic states, by performing numerical optimization of the fidelity, success probability, and Fisher-information functions. For the first time, we have provided convincing numerical evidence that for the basic CNOT (CS) gate the maximal success probability is S = 2/27. We have numerically verified a hypothesis that maximal success probability is achieved using a minimal level of ancilla resource (for NS, CS and Toffoli gates). As a proof of principle, we demonstrated that heuristic methods of constructing optimal optical schemes are quite limited when it comes to complicated 3- and more qubit gates: using the Toffoli gate, we found a scheme that uses fewer ancilla photons and provides better success probability than the best previously known scheme.The numerical optimization method was used to address the error-correction problem. For a particular error-correction scheme, the encoding-decoding gates required construction of a CS gate coupling hyper-entangled qubits. The solution found numerically requires only three ancilla photons while providing maximal success probability. We will also report on our numerical results for optimization of Heisenberg-limited quantum phase metrology.