592 research outputs found
Bounding quantum gate error rate based on reported average fidelity
Remarkable experimental advances in quantum computing are exemplified by
recent announcements of impressive average gate fidelities exceeding 99.9% for
single-qubit gates and 99% for two-qubit gates. Although these high numbers
engender optimism that fault-tolerant quantum computing is within reach, the
connection of average gate fidelity with fault-tolerance requirements is not
direct. Here we use reported average gate fidelity to determine an upper bound
on the quantum-gate error rate, which is the appropriate metric for assessing
progress towards fault-tolerant quantum computation, and we demonstrate that
this bound is asymptotically tight for general noise. Although this bound is
unlikely to be saturated by experimental noise, we demonstrate using explicit
examples that the bound indicates a realistic deviation between the true error
rate and the reported average fidelity. We introduce the Pauli distance as a
measure of this deviation, and we show that knowledge of the Pauli distance
enables tighter estimates of the error rate of quantum gates.Comment: New Journal of Physics Fast Track Communication. Gold open access
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Efficient estimation of resonant coupling between quantum systems
We present an efficient method for the characterization of two coupled discrete quantum systems, one of which can be controlled and measured. For two systems with transition frequencies ωq, ωr, and coupling strength g we show how to obtain estimates of g and ωr whose error decreases exponentially in the number of measurement shots rather than as a power law expected in simple approaches. Our algorithm can thereby identify g and ωr simultaneously with high precision in a few hundred measurement shots. This is achieved by adapting measurement settings upon data as it is collected. We also introduce a method to eliminate erroneous estimates with small overhead. Our algorithm is robust against the presence of relaxation and typical noise. Our results are applicable to many candidate technologies for quantum computation, in particular, for the characterization of spurious two-level systems in superconducting qubits or stripline resonators.5 page(s
Entanglement in quantum field theory via wavelet representations
Quantum field theory (QFT) describes nature using continuous fields, but
physical properties of QFT are usually revealed in terms of measurements of
observables at a finite resolution. We describe a multiscale representation of
a free scalar bosonic and Ising model fermionic QFTs using wavelets. Making use
of the orthogonality and self similarity of the wavelet basis functions, we
demonstrate some well known relations such as scale dependent subsystem
entanglement entropy and renormalization of correlations in the ground state.
We also find some new applications of the wavelet transform as a compressed
representation of ground states of QFTs which can be used to illustrate quantum
phase transitions via fidelity overlap and holographic entanglement of
purification.Comment: 17 pages, 10 figure
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