3,193 research outputs found
Quantum error correction for continuously detected errors
We show that quantum feedback control can be used as a quantum error
correction process for errors induced by weak continuous measurement. In
particular, when the error model is restricted to one, perfectly measured,
error channel per physical qubit, quantum feedback can act to perfectly protect
a stabilizer codespace. Using the stabilizer formalism we derive an explicit
scheme, involving feedback and an additional constant Hamiltonian, to protect
an ()-qubit logical state encoded in physical qubits. This works for
both Poisson (jump) and white-noise (diffusion) measurement processes. In
addition, universal quantum computation is possible in this scheme. As an
example, we show that detected-spontaneous emission error correction with a
driving Hamiltonian can greatly reduce the amount of redundancy required to
protect a state from that which has been previously postulated [e.g., Alber
\emph{et al.}, Phys. Rev. Lett. 86, 4402 (2001)].Comment: 11 pages, 1 figure; minor correction
Resource Optimized Quantum Architectures for Surface Code Implementations of Magic-State Distillation
Quantum computers capable of solving classically intractable problems are
under construction, and intermediate-scale devices are approaching completion.
Current efforts to design large-scale devices require allocating immense
resources to error correction, with the majority dedicated to the production of
high-fidelity ancillary states known as magic-states. Leading techniques focus
on dedicating a large, contiguous region of the processor as a single
"magic-state distillation factory" responsible for meeting the magic-state
demands of applications. In this work we design and analyze a set of optimized
factory architectural layouts that divide a single factory into spatially
distributed factories located throughout the processor. We find that
distributed factory architectures minimize the space-time volume overhead
imposed by distillation. Additionally, we find that the number of distributed
components in each optimal configuration is sensitive to application
characteristics and underlying physical device error rates. More specifically,
we find that the rate at which T-gates are demanded by an application has a
significant impact on the optimal distillation architecture. We develop an
optimization procedure that discovers the optimal number of factory
distillation rounds and number of output magic states per factory, as well as
an overall system architecture that interacts with the factories. This yields
between a 10x and 20x resource reduction compared to commonly accepted single
factory designs. Performance is analyzed across representative application
classes such as quantum simulation and quantum chemistry.Comment: 16 pages, 14 figure
Pair-cat codes: autonomous error-correction with low-order nonlinearity
We introduce a driven-dissipative two-mode bosonic system whose reservoir
causes simultaneous loss of two photons in each mode and whose steady states
are superpositions of pair-coherent/Barut-Girardello coherent states. We show
how quantum information encoded in a steady-state subspace of this system is
exponentially immune to phase drifts (cavity dephasing) in both modes.
Additionally, it is possible to protect information from arbitrary photon loss
in either (but not simultaneously both) of the modes by continuously monitoring
the difference between the expected photon numbers of the logical states.
Despite employing more resources, the two-mode scheme enjoys two advantages
over its one-mode cat-qubit counterpart with regards to implementation using
current circuit QED technology. First, monitoring the photon number difference
can be done without turning off the currently implementable dissipative
stabilizing process. Second, a lower average photon number per mode is required
to enjoy a level of protection at least as good as that of the cat-codes. We
discuss circuit QED proposals to stabilize the code states, perform gates, and
protect against photon loss via either active syndrome measurement or an
autonomous procedure. We introduce quasiprobability distributions allowing us
to represent two-mode states of fixed photon number difference in a
two-dimensional complex plane, instead of the full four-dimensional two-mode
phase space. The two-mode codes are generalized to multiple modes in an
extension of the stabilizer formalism to non-diagonalizable stabilizers. The
-mode codes can protect against either arbitrary photon losses in up to
modes or arbitrary losses and gains in any one mode.Comment: 29 pages, 9 figures, 2 tables; added a numerical compariso
- …