Spin-based quantum gating with semiconductor quantum dots by bichromatic radiation method

– A potential scheme is proposed for realizing a two-qubit quantum gate in semiconductor quantum dots. Information is encoded in the spin degrees of freedom of one excess conduction electron of each quantum dot. We propose to use two lasers, radiating two neighboring QDs, and tuned to blue detuning with respect to the resonant frequencies of individual excitons. The two-qubit phase gate can be achieved by means of both Pauli-blocking effect and dipole-dipole coupling between intermediate excitonic states. Quantum computing with semiconductor quantum dots (QDs) has drawn more and more interest over the past few years [1]. Besides the ease of scalability, semiconductor QD quantum computing is more appealing than other quantum computing schemes due to the existence of the industrial basis for semiconductor processing as well as the promise of being easily integrable. In the schemes for quantum computing with semiconductor QDs proposed so far, either the excitonic or spin degrees of freedom have been identified as potential qubits. Quantum gating based on excitons, although being strongly restricted by the short decoherence time of the exciton, can be implemented ultrafastly with optical manipulations [2]. In contrast, spin qubits, due to their relatively long decoherence time [3,4], allow for longer storage of quantum information. Quantum gates can be carried out by means of Coulomb interaction [2, 5–7] or by coupling to a cavity mode [4, 8, 9]. When nearest-neighbor coupling plays an important role, one has to face a significant overhead for coupling two distant QDs. On the contrary, if the QDs are put into a cavity, two distant QDs can interact directly through coupling to the same cavity mode. Nevertheless, the implementation time in such a model is typically quite long due to both the large detuning technique adopted for avoiding the cavity decay and the weak cavity-laser-QD coupling [9].