Abstract
In double quantum dot singlet–triplet qubits, the exchange interaction is used in both quantum gate operation and the measurement of the state of the qubit. The exchange can be controlled electronically by applying gate voltage pulses. We simulate the exchange induced charge state transitions in one and two singlet–triplet qubit systems using the exact diagonalization method. We find that fast detuning pulses may result in leakage between different singlet charge states. The leakage could cause measurement errors and hinder quantum gate operation for example in the case of the two-qubit Coulomb gate.
Highlights
The development of experimental methods has enabled the fabrication of ‘artificial atoms’ with a controlled number of electrons, ranging from a few to a few hundred, confined in a tunable external potential inside a semiconductor [1,2,3]
A singlet–triplet qubit is modeled with a double QD (DQD) potential
It is effectively similar to the one qubit case shown in figure 3, as the T0 part is not affected by the detuning
Summary
The development of experimental methods has enabled the fabrication of ‘artificial atoms’ with a controlled number of electrons, ranging from a few to a few hundred, confined in a tunable external potential inside a semiconductor [1,2,3]. The universal set of quantum gates for two spin singlet–triplet DQD qubits has been demonstrated experimentally These gates include one qubit rotations generated by the exchange interaction [8], stabilized hyperfine magnetic field gradients [9] and two qubit operations using long distance capacitative coupling by the Coulomb interaction [10, 11]. We study the effect of the speed of the detuning sweep and find that a fast increase can lead to Landau–Zener type leakage between the charge states. We propose that this kind of leakage could cause errors in measuring the singlet probability. We study the operation of the capacitatively coupling Coulomb gate and discover that the leakage may result in the gate not achieving maximal Bell-state entanglement
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