Abstract
The electron exchange interaction is a promising medium for the entanglement of single-spin qubits in semiconductors as it results in high-speed two-qubit gates. The quality of such entangling gates is reduced by the presence of noise caused by nearby defects acting as two-level fluctuators. To date, the effect of charge noise has been calculated assuming a Gaussian distribution of exchange interaction frequencies between the qubits equivalent to a linear coupling of charge noise with the exchange interaction. In reality the coupling can differ significantly from this linear-coupling approximation depending on the inter-qubit tunnel coupling, detuning of the qubit system, and the magnitude of charge noise. We derive analytical expressions for the frequency spectra of exchange oscillations that encompasses both linear and non-linear coupling to charge-noise. The resulting decoherence times and decay profiles of the exchange oscillations vary considerably. When compared with recent experiments our model shows that non-linear charge-noise coupling is significant and requires consideration to characterise and optimise exchange-based entangling gates.
Highlights
To achieve universal quantum computation with error correction, all qubit operations including initialisation, single- and two-qubit gates, and measurement require errors to be less than 1%1,2
In this work we model the coherent time evolution of a pair of electron spins due to this distribution of exchange interaction strengths caused by the presence of charge noise tw =
When considering the charge noise arising from a nearby ensemble of two-level fluctuators (TLFs), one would expect the distribution of charge noise to be Gaussian[16,17]
Summary
To achieve universal quantum computation with error correction, all qubit operations including initialisation, single- and two-qubit gates, and measurement require errors to be less than 1%1,2. We identify when these effects differ significantly from the linear coupling case This identification allows us to consider how to account for coupling to charge noise in exchange-based qubits under different operating regimes which ensures that the appropriate model is used to characterise coherent exchange oscillations in multi-qubit systems. Exchange-based two-qubit operations in semiconductor qubits are performed on single electron spins by sweeping the detuning potential ε of a double-dot system across a (1,1) to (2,0). The left and right numbers correspond to the ground state electron numbers on the left and right dots respectively This charge transition forms an anticrossing between the S(1,1) and S(2,0) singlet spin states whose ground state energy levels are depicted in Fig. 1 along with the triplet T0 state. The two-spin system near the anti-crossing is described in the two-spin product basis (j""i; j"#i; j#"i; j##i) by the Hamiltonian H,
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