53 research outputs found
Error- and Loss-Tolerances of Surface Codes with General Lattice Structures
We propose a family of surface codes with general lattice structures, where
the error-tolerances against bit and phase errors can be controlled
asymmetrically by changing the underlying lattice geometries. The surface codes
on various lattices are found to be efficient in the sense that their threshold
values universally approach the quantum Gilbert-Varshamov bound. We find that
the error-tolerance of surface codes depends on the connectivity of underlying
lattices; the error chains on a lattice of lower connectivity are easier to
correct. On the other hand, the loss-tolerance of surface codes exhibits an
opposite behavior; the logical information on a lattice of higher connectivity
has more robustness against qubit loss. As a result, we come upon a fundamental
trade-off between error- and loss-tolerances in the family of the surface codes
with different lattice geometries.Comment: 5pages, 3 figure
Optimal cavity design for minimizing errors in cavity-QED-based atom-photon entangling gates with finite temporal duration
We investigate atom-photon entangling gates based on cavity quantum
electrodynamics (QED) for a finite photon-pulse duration, where not only the
photon loss but also the temporal mode-mismatch of the photon pulse becomes a
severe source of error. We analytically derive relations between cavity
parameters, including transmittance, length, and effective cross-sectional area
of the cavity, that minimize both the photon loss probability and the error
rate due to temporal mode-mismatch by taking it into account as state-dependent
pulse delay. We also investigate the effects of pulse distortion using
numerical simulations for the case of short pulse duration.Comment: 8 pages, 5 figure
Virtual quantum error detection
Quantum error correction and quantum error detection necessitate syndrome
measurements to detect errors. Performing syndrome measurements for each
stabilizer generator can be a significant overhead, considering the fact that
the readout fidelity in the current quantum hardware is generally lower than
gate fidelity. Here, by generalizing a quantum error mitigation method known as
symmetry expansion, we propose a protocol called virtual quantum error
detection (VQED). This method virtually allows for evaluating computation
results corresponding to post-selected quantum states obtained through quantum
error detection during circuit execution, without implementing syndrome
measurements. Unlike conventional quantum error detection, which requires the
implementation of Hadamard test circuits for each stabilizer generator, our
VQED protocol can be performed with a constant depth shallow quantum circuit
with an ancilla qubit, irrespective of the number of stabilizer generators.
Furthermore, for some simple error models, the computation results obtained
using VQED are robust against the noise that occurred during the operation of
VQED, and our method is fully compatible with other error mitigation schemes,
enabling further improvements in computation accuracy and facilitating
high-fidelity quantum computing.Comment: 10 pages, 8 figures, 1 tabl
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