Demonstration of a Photon-atom SWAP Gate

Deterministic quantum interactions between single photons and single quantum emitters can serve as a valuable building block for the distribution of quantum information between remote systems. Deterministic photon-atom state transfer has so far been demonstrated by using protocols that include synchronized control pulses or active feedback. In this talk I will present our recent demonstration of a completely passive swap gate between the states of a single photon and a single atom [1]. The underlying mechanism is single-photon Raman interaction (SPRINT) - an interference-based effect in which a photonic qubit deterministically controls the state of a material qubit encoded in the two ground states of a Lambda system, and vice versa [2-4]. In our system we use a nanofiber-coupled microsphere resonator coupled to single Rb atoms to demonstrate swapping of a photonic qubit into the atom and back, attaining nonclassical fidelities in both directions. This open-system scheme is applicable to any waveguide-coupled Lambda system (it has been also demonstrated in microwave with superconducting qubits [5-6]) and can serve as a basis for a variety of other photon-"atom" interactions - from universal gates, through QND measurement, to the preparations of nonclassical states of light such as single-photon subtracted or added states, Fock states and cat states. All these interactions takes place "automatically" at the timescale of the cavity-enhanced spontaneous emission time. Requiring no control fields or feedback protocol, this scheme provides a versatile building block for the modular scaling up of quantum information processing systems.

[1] Nature Physics 14, (2018)

[2] Science 345, 903 (2014)

[3] Nature Photonics 10, 19 (2016)

[4] Phys. Rev. A 95, 0333814 (2017)

[5] Phys. Rev. Lett. 113, 0636104 (2014)

[6] Nature Communications 7, 1 (2016)