243,556 research outputs found
Decoherence-based exploration of d-dimensional one-way quantum computation
We study the effects of amplitude and phase damping decoherence in
d-dimensional one-way quantum computation (QC). Our investigation shows how
information transfer and entangling gate simulations are affected for d>=2. To
understand motivations for extending the one-way model to higher dimensions, we
describe how d-dimensional qudit cluster states deteriorate under environmental
noise. In order to protect quantum information from the environment we consider
the encoding of logical qubits into physical qudits and compare entangled pairs
of linear qubit-cluster states with single qudit clusters of equal length and
total dimension. Our study shows a significant reduction in the performance of
one-way QC for d>2 in the presence of Markovian type decoherence models.Comment: 8 pages, 11 figures, RevTeX
Noise analysis of single-qumode Gaussian operations using continuous-variable cluster states
We consider measurement-based quantum computation that uses scalable
continuous-variable cluster states with a one-dimensional topology. The
physical resource, known here as the dual-rail quantum wire, can be generated
using temporally multiplexed offline squeezing and linear optics or by using a
single optical parametric oscillator. We focus on an important class of quantum
gates, specifically Gaussian unitaries that act on single modes, which gives
universal quantum computation when supplemented with multi-mode operations and
photon-counting measurements. The dual-rail wire supports two routes for
applying single-qumode Gaussian unitaries: the first is to use traditional
one-dimensional quantum-wire cluster-state measurement protocols. The second
takes advantage of the dual-rail quantum wire in order to apply unitaries by
measuring pairs of qumodes called macronodes. We analyze and compare these
methods in terms of the suitability for implementing single-qumode Gaussian
measurement-based quantum computation.Comment: 25 pages, 9 figures, more accessible to general audienc
Resource Requirements for Fault-Tolerant Quantum Simulation: The Transverse Ising Model Ground State
We estimate the resource requirements, the total number of physical qubits
and computational time, required to compute the ground state energy of a 1-D
quantum Transverse Ising Model (TIM) of N spin-1/2 particles, as a function of
the system size and the numerical precision. This estimate is based on
analyzing the impact of fault-tolerant quantum error correction in the context
of the Quantum Logic Array (QLA) architecture. Our results show that due to the
exponential scaling of the computational time with the desired precision of the
energy, significant amount of error correciton is required to implement the TIM
problem. Comparison of our results to the resource requirements for a
fault-tolerant implementation of Shor's quantum factoring algorithm reveals
that the required logical qubit reliability is similar for both the TIM problem
and the factoring problem.Comment: 19 pages, 8 figure
Thermalization, Error-Correction, and Memory Lifetime for Ising Anyon Systems
We consider two-dimensional lattice models that support Ising anyonic
excitations and are coupled to a thermal bath. We propose a phenomenological
model for the resulting short-time dynamics that includes pair-creation,
hopping, braiding, and fusion of anyons. By explicitly constructing topological
quantum error-correcting codes for this class of system, we use our
thermalization model to estimate the lifetime of the quantum information stored
in the encoded spaces. To decode and correct errors in these codes, we adapt
several existing topological decoders to the non-Abelian setting. We perform
large-scale numerical simulations of these two-dimensional Ising anyon systems
and find that the thresholds of these models range between 13% to 25%. To our
knowledge, these are the first numerical threshold estimates for quantum codes
without explicit additive structure.Comment: 34 pages, 9 figures; v2 matches the journal version and corrects a
misstatement about the detailed balance condition of our Metropolis
simulations. All conclusions from v1 are unaffected by this correctio
Spin-based all-optical quantum computation with quantum dots: understanding and suppressing decoherence
We present an all-optical implementation of quantum computation using
semiconductor quantum dots. Quantum memory is represented by the spin of an
excess electron stored in each dot. Two-qubit gates are realized by switching
on trion-trion interactions between different dots. State selectivity is
achieved via conditional laser excitation exploiting Pauli exclusion principle.
Read-out is performed via a quantum-jump technique. We analyze the effect on
our scheme's performance of the main imperfections present in real quantum
dots: exciton decay, hole mixing and phonon decoherence. We introduce an
adiabatic gate procedure that allows one to circumvent these effects, and
evaluate quantitatively its fidelity
Information gap for classical and quantum communication in a Schwarzschild spacetime
Communication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
Extending the memory times of trapped-ion qubits with error correction and global entangling operations
The technical demands to perform quantum error correction are considerable.
The task requires the preparation of a many-body entangled state, together with
the ability to make parity measurements over subsets of the physical qubits of
the system to detect errors. Here we propose two trapped-ion experiments to
realise error-correcting codes of variable size to protect a single encoded
qubit from dephasing errors. Novel to our schemes is the use of a global
entangling phase gate, which could be implemented in both Penning traps and
Paul traps. We make use of this entangling operation to significantly reduce
the experimental complexity of state preparation and syndrome measurements. We
also show, in our second scheme, that storage times can be increased further by
repeatedly teleporting the logical information between two codes supported by
the same ion Coulomb crystal to learn information about the locations of
errors. We estimate that a logical qubit encoded in such a crystal will
maintain high coherence for times more than an order of magnitude longer than
each physical qubit would.Comment: 18 pages, 8 figures. The authors list has changed since the first
version of this draf
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