268 research outputs found
Leakage-current lineshapes from inelastic cotunneling in the Pauli spin blockade regime
We find the leakage current through a double quantum dot in the Pauli spin
blockade regime accounting for inelastic (spin-flip) cotunneling processes.
Taking the energy-dependence of this spin-flip mechanism into account allows
for an accurate description of the current as a function of applied magnetic
fields, gate voltages, and an inter-dot tunnel coupling. In the presence of an
additional local dephasing process or nonuniform magnetic field, we obtain a
simple closed-form analytical expression for the leakage current giving the
full dependence on an applied magnetic field and energy detuning. This work is
important for understanding the nature of leakage, especially in systems where
other spin-flip mechanisms (due, e.g., to hyperfine coupling to nuclear spins
or spin-orbit coupling) are weak, including silicon and carbon-nanotube or
graphene quantum dots.Comment: 11 pages, 10 figures; v2: Typos corrected, colorbar added to fig. 7,
final version published in Phys. Rev.
Enhancing qubit readout through dissipative sub-Poissonian dynamics
Single-shot qubit readout typically combines high readout contrast with
long-lived readout signals, leading to large signal-to-noise ratios and high
readout fidelities. In recent years, it has been demonstrated that both readout
contrast and readout signal lifetime, and thus the signal-to-noise ratio, can
be enhanced by forcing the qubit state to transition through intermediate
states. In this work, we demonstrate that the sub-Poissonian relaxation
statistics introduced by intermediate states can reduce the single-shot readout
error rate by orders of magnitude even when there is no increase in
signal-to-noise ratio. These results hold for moderate values of the
signal-to-noise ratio () and a small number of
intermediate states (). The ideas presented here could have
important implications for readout schemes relying on the detection of
transient charge states, such as spin-to-charge conversion schemes for
semiconductor spin qubits and parity-to-charge conversion schemes for
topologically protected Majorana qubits.Comment: 10 pages, 6 figures. Two appendices have been added. This version is
close to the final published versio
Exchange-controlled single-electron-spin rotations in quantum dots
We show theoretically that arbitrary coherent rotations can be performed
quickly (with a gating time ~1 ns) and with high fidelity on the spin of a
single confined electron using control of exchange only, without the need for
spin-orbit coupling or ac fields. We expect that implementations of this scheme
would achieve gate error rates on the order of \eta ~ 10^{-3} in GaAs quantum
dots, within reach of several known error-correction protocolsComment: 4+ pages, 3 figures; v2: Streamlined presentation, final version
published in PRB (Rapid Comm.
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