258 research outputs found
Configuration interaction calculations of the controlled phase gate in double quantum dot qubits
We consider qubit coupling resulting from the capacitive coupling between two
double quantum dot (DQD) single-triplet qubits. Calculations of the coupling
when the two DQDs are detuned symmetrically or asymmetrically are performed
using a full configuration interaction (CI). The full CI reveals behavior that
is not observed by more commonly used approximations such as Heitler London or
Hund Mulliken, particularly related to the operation of both DQDs in the (0,2)
charge sector. We find that there are multiple points in detuning-space where a
two-qubit entangling gate can be realized, and that trade-offs between coupling
magnitude and sensitivity to fluctuations in detuning make a case for operating
the gate in the (0,2) regime not commonly considered.Comment: 4 pages, 5 figure
High-fidelity single-shot readout for a spin qubit via an enhanced latching mechanism
The readout of semiconductor spin qubits based on spin blockade is fast but
suffers from a small charge signal. Previous work suggested large benefits from
additional charge mapping processes, however uncertainties remain about the
underlying mechanisms and achievable fidelity. In this work, we study the
single-shot fidelity and limiting mechanisms for two variations of an enhanced
latching readout. We achieve average single-shot readout fidelities > 99.3% and
> 99.86% for the conventional and enhanced readout respectively, the latter
being the highest to date for spin blockade. The signal amplitude is enhanced
to a full one-electron signal while preserving the readout speed. Furthermore,
layout constraints are relaxed because the charge sensor signal is no longer
dependent on being aligned with the conventional (2, 0) - (1, 1) charge dipole.
Silicon donor-quantum-dot qubits are used for this study, for which the dipole
insensitivity substantially relaxes donor placement requirements. One of the
readout variations also benefits from a parametric lifetime enhancement by
replacing the spin-relaxation process with a charge-metastable one. This
provides opportunities to further increase the fidelity. The relaxation
mechanisms in the different regimes are investigated. This work demonstrates a
readout that is fast, has one-electron signal and results in higher fidelity.
It further predicts that going beyond 99.9% fidelity in a few microseconds of
measurement time is within reach.Comment: Supplementary information is included with the pape
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