We propose a photonic CPHASE gate based on Kerr nonlinearities and tunable cavities enabling complete absorption and re-emission of photons. Storing photons about 40 times the width of their wavepackets results in 99% gate fidelity.
We report the construction of a passive, deterministic and near-unity-fidelity controlled-π-phase gate for single-photon wavepackets with a node comprising a two-level emitter and a small number of cavities. The proposed gate is rooted in the concept of time-reversal symmetric photon transport, which makes the entire photon transport process into a perfect absorption and re-emission process. Consequently, it can circumvent the longstanding issue of wavepacket distortion inherent in photonic phase gates employing nonlinear media. Moreover, such time-reversal symmetric transport ensures the nonlinear π phase shift by a single two-level emitter for the two-photon case. We develop analytical solutions to reveal the temporal dynamics of the nonlinear photon transport and to optimize the gate structure. Notably, the gate fidelity can exceed 99\% for a node with only four cavities for both single-photon and two-photon operations. Moreover, the proposed gate architecture is compatible with the platforms of integrated photonics.
We show that relatively simple integrated photonic circuits have the potential to realize a high fidelity deterministic controlled-phase gate between photonic qubits using bulk optical nonlinearities. The gate is enabled by converting travelling continuous-mode photons into stationary cavity modes using strong classical control fields that dynamically change the effective cavity-waveguide coupling rate. This architecture succeeds because it reduces the wave packet distortions that otherwise accompany the action of optical nonlinearities [J. Shapiro, Phys. Rev. A 73, 062305 (2006)PLRAAN1050-294710.1103/PhysRevA.73.062305; J. Gea-Banacloche, Phys. Rev. A 81, 043823 (2010)PLRAAN1050-294710.1103/PhysRevA.81.043823]. We show that high-fidelity gates can be achieved with self-phase modulation in χ^{(3)} materials as well as second-harmonic generation in χ^{(2)} materials. The gate fidelity asymptotically approaches unity with increasing storage time for an incident photon wave packet with fixed duration. We also show that dynamically coupled cavities enable a trade-off between errors due to loss and wave packet distortion. Our proposed architecture represents a new approach to practical implementation of quantum gates that is room-temperature compatible and only relies on components that have been individually demonstrated.
We propose a scheme for high-fidelity photonic controlled-phase gates using a Rydberg blockade in an ensemble of atoms in an optical cavity. The gate operation is obtained by first storing a photonic pulse in the ensemble and then scattering a second pulse from the cavity, resulting in a phase change depending on whether the first pulse contained a single photon. We show that the combination of a Rydberg blockade and optical cavities effectively enhances the optical nonlinearity created by the strong Rydberg interaction and makes the gate operation more robust. The resulting gate can be implemented with cavities of moderate finesse, allowing for highly efficient processing of quantum information encoded in photons. As an illustration, we show how the gate can be employed to increase the communication rate of quantum repeaters based on atomic ensembles.
A central goal in photonic quantum information processing is the ability to perform high-fidelity logic gates between multiple optical qubits. Here, we present our recent theoretical work on using optical nonlinearities to implement controlled-phase gates between two optical qubits. Our approach is based on using dynamically coupled cavities to convert photons travelling in a waveguide into highly confined cavity modes. This conversion enables very strong interactions between photons in quasi-monochromatic modes, which enables high fidelity gates. We will discuss gate protocols based on second- and third order nonlinear materials as well as interactions with two-level emitters.