Robust entangling gate for capacitively coupled few-electron singlet-triplet qubits

Abstract

The search of a sweet spot, locus in qubit parameters where quantum control is first-order insensitive to noises, is key to achieve high-fidelity quantum gates. Efforts to search for such a sweet spot in conventional double-quantum-dot singlet-triplet qubits where each dot hosts one electron ("two-electron singlet-triplet qubit"), especially for two-qubit operations, have been unsuccessful. Here we consider singlet-triplet qubits allowing each dot to host more than one electron, with a total of four electrons in the double quantum dots ("four-electron singlet-triplet qubit"). We theoretically demonstrate, using configuration-interaction calculations, that sweet spots appear in this coupled qubit system. We further demonstrate that, under realistic charge noise and hyperfine noise, two-qubit operation at the proposed sweet spot could offer gate fidelities (∼ 99%) that are higher than conventional two-electron singlet-triplet qubit system (∼ 90%). Our results should facilitate realization of high-fidelity two-qubit gates in singlet-triplet qubit systems.

Theory on electron-phonon spin dehphasing in GaAs multi-electron double quantum dots

“…It has also been observed in a similar system that the sign of the exchange energy may reverse, removing a long-standing constraint for the construction of dynamically corrected exchange gates [37]. On the theory side, calculations based on the Configuration Interaction (CI) techniques on few-electron multi-quantum-dot systems have demonstrated negative exchange interactions and their implication on robust quantum control [43][44][45]. Other studies on these systems have unveiled their potentials for tunable couplings [30], robust quantum gates [41], as well as other interesting properties [42].…”

“…In double quantum dots (DQD) hosting two electrons, it has been shown that the deformation potential and piezoelectric interaction play major roles in the electron-phonon dephasing, and all channels of phonon couplings reduce as the dot distance increases [48,49]. It is an interesting open question how the behavior of the electron-phonon dephasing may change as the number of electrons in the DQD is increased [45].…”