Two-qubit quantum gates for defect qubits in diamond and similar systems

Abstract

We propose a fast, scalable all-optical design for arbitrary two-qubit operations for defect qubits in diamond (NV centers) and in silicon carbide, which are promising candidates for room temperature quantum computing. The interaction between qubits is carried out by microcavity photons. The approach uses constructive interference from higher energy excited states activated by optical control. In this approach the cavity mode remains off-resonance with the directly accessible optical transitions used for initialization and readout. All quantum operations are controlled by near-resonant narrow-bandwidth optical pulses. We perform full quantum numerical modeling of the proposed gates and show that high-fidelity operations can be obtained with realistic parameters

Resource requirements for efficient quantum communication using all-photonic graph states generated from a few matter qubits

“…Currently, most of the two-qubit gates that have been experimentally demonstrated are slow because they rely on local interactions, such as the hyperfine coupling, which are generally weak. Efficient light-matter interfaces using cavities can also be used to realize deterministic, photon-mediated CZ gates between two matter qubits [70], using spin-photon gates [77][78][79]. The crucial advantage of this technique is that it only requires optical interactions, which are intrinsically much faster than hyperfine interactions.…”

“…Here, we have made the simplifying assumption that the main source of infidelity is the matter qubit decoherence, and we have assumed that the effect of this decoherence is to reduce the overall [69][70][71] 99.2% [72] 0.6s [73] 99% [23] Trapped ions 10µs [74] 99.9% [74] 10min [75] 89% [76] Table 3: State-of-the-art characteristics of candidate quantum emitters. T CZ is the duration of a CZ gate, T 2 is the coherence time, β is the single-mode photon emission probability, and F the two-qubit gate fidelity.…”

Designing a cavity-mediated quantum cphase gate between NV spin qubits in diamond

“…In contrast to cavity-mediated spin interactions proposed for semiconductor quantum dots 13 where the spinorbit splitting in the valence band can be used for spinselective excitation with polarized radiation and Ramantype spin flip transitions, we propose here to use another mechanism based on the different zero-field splittings of the NV ground and excited states to perform phase and controlled-phase operations. Earlier work on cavity-mediated quantum gates for defect qubits in diamond makes use of spectral hole burning 14 or a series of Λ systems 15 . The latter requires a sequence of at least three two-color pulses, while our scheme manages on just one single-color laser pulse for a CPHASE gate.…”

Quantum gates via continuous time quantum walks in multiqubit systems with non-local auxiliary states

“…Because quantum walk pulses can involve multiple non-equal Rabi frequencies that are effectively "multiplied" by the time duration t n 2 − t n 1 of each pulse, some specific convention must be adopted to compare the duration of gates performed this way to the duration of gates or gate decompositions performed by single-frequency pulses. 7,21,22 For this purpose, it is natural to limit the maximum Rabi frequency of each pulse (pulse field amplitude) to some value accessible to specific experimental setup (and the same for all pulses) and adjust t n 2 − t n 1 to produce entries of the desired magnitude in each τ n Λ n matrix.…”

“…As the result, local single-qubit gates and non-local entanglement manipulations can be performed by pulses without changing the strength of interactions or shifting qubits' energy levels dynamically. 7,21,22 Unfortunately, the intermediate resonance regime in the single-cavity system is not scalable beyond several qubits due to spectral crowding that hinders the distinguishability of states for realistic values of pulse bandwidth. 23 In the following subsections we will show how symmetry breaking in relations (20) can occur for a scalable multiqubit register.…”