Nondestructive detection of photonic qubits.

ABSTRACT: One of the biggest challenges in experimental quantum information is to sustain the fragile superposition state of a qubit¹. Long lifetimes can be achieved for material qubit carriers as memories², at least in principle, but not for propagating photons that are rapidly lost by absorption, diffraction or scattering³. The loss problem can be mitigated with a nondestructive photonic qubit detector that heralds the photon without destroying the encoded qubit. Such a detector is envisioned to facilitate protocols in which distributed tasks depend on the successful dissemination of photonic qubits^4,5, improve loss-sensitive qubit measurements^6,7 and enable certain quantum key distribution attacks⁸. Here we demonstrate such a detector based on a single atom in two crossed fibre-based optical resonators, one for qubit-insensitive atom-photon coupling and the other for atomic-state detection⁹. We achieve a nondestructive detection efficiency upon qubit survival of 79 ± 3 per cent and a photon survival probability of 31 ± 1 per cent, and we preserve the qubit information with a fidelity of 96.2 ± 0.3 per cent. To illustrate the potential of our detector, we show that it can, with the current parameters, improve the rate and fidelity of long-distance entanglement and quantum state distribution compared to previous methods, provide resource optimization via qubit amplification and enable detection-loophole-free Bell tests.

SUBMITTER: Niemietz D 

PROVIDER: S-EPMC7990738 | biostudies-literature |

REPOSITORIES: biostudies-literature