8,120 research outputs found
Short-Time Decoherence and Deviation from Pure Quantum States
In systems considered for quantum computing, i.e., for control of quantum
dynamics with the goal of processing information coherently, decoherence and
deviation from pure quantum states, are the main obstacles to fault-tolerant
error correction. At low temperatures, usually assumed in quantum computing
designs, some of the accepted approaches to evaluation of relaxation mechanisms
break down. We develop a new general formalism for estimation of decoherence at
short times, appropriate for evaluation of quantum computing architectures.Comment: 9 pages in plain Te
Fault-tolerant protection of near-term trapped-ion topological qubits under realistic noise sources
The quest of demonstrating beneficial quantum error correction in near-term
noisy quantum processors can benefit enormously from a low-resource
optimization of fault-tolerant schemes, which are specially designed for a
particular platform considering both state-of-the-art technological
capabilities and main sources of noise. In this work, we show that
flag-qubit-based fault-tolerant techniques for active error detection and
correction, as well as for encoding of logical qubits, can be leveraged in
current designs of trapped-ion quantum processors to achieve this break-even
point of beneficial quantum error correction. Our improved description of the
relevant sources of noise, together with detailed schedules for the
implementation of these flag-based protocols, provide one of the most complete
microscopic characterizations of a fault-tolerant quantum processor to date. By
extensive numerical simulations, we provide a comparative study of flag- and
cat-based approaches to quantum error correction, and show that the superior
performance of the former can become a landmark in the success of near-term
quantum computing with noisy trapped-ion devices.Comment: new version, accepted in Phys. Rev.
Fault-tolerant linear optical quantum computing with small-amplitude coherent states
Quantum computing using two optical coherent states as qubit basis states has
been suggested as an interesting alternative to single photon optical quantum
computing with lower physical resource overheads. These proposals have been
questioned as a practical way of performing quantum computing in the short term
due to the requirement of generating fragile diagonal states with large
coherent amplitudes. Here we show that by using a fault-tolerant error
correction scheme, one need only use relatively small coherent state amplitudes
() to achieve universal quantum computing. We study the effects
of small coherent state amplitude and photon loss on fault tolerance within the
error correction scheme using a Monte Carlo simulation and show the quantity of
resources used for the first level of encoding is orders of magnitude lower
than the best known single photon scheme. %We study this reigem using a Monte
Carlo simulation and incorporate %the effects of photon loss in this
simulation
Noise threshold and resource cost of fault-tolerant quantum computing with Majorana fermions in hybrid systems
Fault-tolerant quantum computing in systems composed of both Majorana
fermions and topologically unprotected quantum systems, e.g. superconducting
circuits or quantum dots, is studied in this paper. Errors caused by
topologically unprotected quantum systems need to be corrected with error
correction schemes, for instance, the surface code. We find that the
error-correction performance of such a hybrid topological quantum computer is
not superior to a normal quantum computer unless the topological charge of
Majorana fermions is insusceptible to noise. If errors changing the topological
charge are rare, the fault-tolerance threshold is much higher than the
threshold of a normal quantum computer, and a surface-code logical qubit could
be encoded in only tens of topological qubits instead of about a thousand
normal qubits.Comment: 15 pages, 11 figure
Enhanced fault-tolerant quantum computing in -level systems
Error correcting codes protect quantum information and form the basis of
fault tolerant quantum computing. Leading proposals for fault-tolerant quantum
computation require codes with an exceedingly rare property, a transverse
non-Clifford gate. Codes with the desired property are presented for -level,
qudit, systems with prime . The codes use qudits and can detect upto
errors. We quantify the performance of these codes for one approach
to quantum computation, known as magic state distillation. Unlike prior work,
we find performance is always enhanced by increasing .Comment: Author's final copy. Changes includes correction to plot in figure
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