Section: New Results

Loss-tolerant parity measurement for distant quantum bits

Participants: A. Sarlette, M. Mirrahimi

This work, published in [17], [24], is part of the major line of work led by M.Mirrahimi about stabilizing distant entangled states. The latter are a major building block in quantum information technology, thanks to their ability to enable quantum teleportation. They are supposed to play a major 'quantum-bus-type' role in some of the most promising quantum computing architectures.

In this paper, we propose a scheme to measure the parity of two distant qubits, while ensuring that losses on the quantum channel between them does not destroy coherences within the parity subspaces. This capability enables deterministic preparation of highly entangled qubit states whose fidelity is not limited by the transmission loss. The key observation is that for a probe electromagnetic field in a particular quantum state, namely a superposition of two coherent states of opposite phases, the transmission loss stochastically applies a near-unitary back-action on the probe state. This leads to a parity measurement protocol where the main effect of the transmission losses is a decrease in the measurement strength. By repeating the non-destructive (weak) parity measurement, one achieves a high-fidelity entanglement in spite of a significant transmission loss.