Magic angle for barrier-controlled double quantum dots

Abstract

We show that the exchange interaction of a singlet-triplet spin qubit confined in double quantum dots, when being controlled by the barrier method, is insensitive to a charged impurity lying along certain directions away from the center of the double-dot system. These directions differ from the polar axis of the double dots by the magic angle, equaling $\arccos \left(1/\sqrt{3}\right)\approx 54.7^{\circ }$, a value previously found in atomic physics and nuclear magnetic resonance. This phenomenon can be understood from an expansion of the additional Coulomb interaction created by the impurity, but also relies on the fact that the exchange interaction solely depends on the tunnel coupling in the barrier-control scheme. Our results suggest that for a scaled-up qubit array, when all pairs of double dots rotate their respective polar axes from the same reference line by the magic angle, cross-talks between qubits can be eliminated, allowing clean single-qubit operations. While our model is a rather simplified version of actual experiments, our results suggest that it is possible to minimize unwanted couplings by judiciously designing the layout of the qubits.

8 pages, 5 figures

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Cited by in corpus (6)

• Negative exchange interactions in coupled few-electron quantum dots
• Theory of barrier vs tilt exchange gate operations in spin-based quantum computing
• Charge noise suppression in capacitively coupled singlet-triplet spin qubits under magnetic field
• Tunable charge qubit based on barrier-controlled triple quantum dots
• Microscopic theory on magnetic-field-tuned sweet spot of exchange interactions in multielectron quantum-dot systems
• Sign-switching of superexchange mediated by few electrons under non-uniform magnetic field