209 research outputs found
Using the J1-J2 Quantum Spin Chain as an Adiabatic Quantum Data Bus
This paper investigates numerically a phenomenon which can be used to
transport a single q-bit down a J1-J2 Heisenberg spin chain using a quantum
adiabatic process. The motivation for investigating such processes comes from
the idea that this method of transport could potentially be used as a means of
sending data to various parts of a quantum computer made of artificial spins,
and that this method could take advantage of the easily prepared ground state
at the so called Majumdar-Ghosh point. We examine several annealing protocols
for this process and find similar result for all of them. The annealing process
works well up to a critical frustration threshold.Comment: 14 pages, 13 figures (2 added), revisions made to add citations and
additional discussion at request of referee
Approximation of quantum control correction scheme using deep neural networks
We study the functional relationship between quantum control pulses in the
idealized case and the pulses in the presence of an unwanted drift. We show
that a class of artificial neural networks called LSTM is able to model this
functional relationship with high efficiency, and hence the correction scheme
required to counterbalance the effect of the drift. Our solution allows
studying the mapping from quantum control pulses to system dynamics and then
analysing the robustness of the latter against local variations in the control
profile.Comment: 6 pages, 3 figures, Python code available upon request. arXiv admin
note: text overlap with arXiv:1803.0516
Quantum gate learning in qubit networks: Toffoli gate without time-dependent control
We put forward a strategy to encode a quantum operation into the unmodulated dynamics of a quantum network without the need for external control pulses, measurements or active feedback. Our optimisation scheme, inspired by supervised machine learning, consists in engineering the pairwise couplings between the network qubits so that the target quantum operation is encoded in the natural reduced dynamics of a network section. The efficacy of the proposed scheme is demonstrated by the finding of uncontrolled four-qubit networks that implement either the Toffoli gate, the Fredkin gate or remote logic operations. The proposed Toffoli gate is stable against imperfections, has a high fidelity for fault-tolerant quantum computation and is fast, being based on the non-equilibrium dynamics
How to enhance quantum generative adversarial learning of noisy information
Quantum Machine Learning is where nowadays machine learning meets quantum
information science. In order to implement this new paradigm for novel quantum
technologies, we still need a much deeper understanding of its underlying
mechanisms, before proposing new algorithms to feasibly address real problems.
In this context, quantum generative adversarial learning is a promising
strategy to use quantum devices for quantum estimation or generative machine
learning tasks. However, the convergence behaviours of its training process,
which is crucial for its practical implementation on quantum processors, have
not been investigated in detail yet. Indeed here we show how different training
problems may occur during the optimization process, such as the emergence of
limit cycles. The latter may remarkably extend the convergence time in the
scenario of mixed quantum states playing a crucial role in the already
available noisy intermediate scale quantum devices. Then, we propose new
strategies to achieve a faster convergence in any operating regime. Our results
pave the way for new experimental demonstrations of such hybrid
classical-quantum protocols allowing to evaluate the potential advantages over
their classical counterparts.Comment: 16 pages, 9 figure
Analytical bounds for non-asymptotic asymmetric state discrimination
Two types of errors can occur when discriminating pairs of quantum states.
Asymmetric state discrimination involves minimising the probability of one type
of error, subject to a constraint on the other. We give explicit expressions
bounding the set of achievable errors, using the trace norm, the fidelity, and
the quantum Chernoff bound. The upper bound is asymptotically tight and the
lower bound is exact for pure states. Unlike asymptotic bounds, our bounds give
error values instead of exponents, so can give more precise results when
applied to finite-copy state discrimination problems.Comment: 11 pages, 2 figure
Continuous variable port-based teleportation
Port-based teleportation is generalization of the standard teleportation
protocol which does not require unitary operations by the receiver. This comes
at the price of requiring entangled pairs, while for the standard
teleportation protocol. The lack of correction unitaries allows port-based
teleportation to be used as a fundamental theoretical tool to simulate
arbitrary channels with a general resource, with applications to study
fundamental limits of quantum communication, cryptography and sensing, and to
define general programmable quantum computers. Here we introduce a general
formulation of port-based teleportation in continuous variable systems and
study in detail the case. In particular, we interpret the resulting
channel as an energy truncation and analyse the kinds of channels that can be
naturally simulated after this restriction.Comment: 27 pages, 6 figures. Similar to published version. Supplemental
material available in the source folde
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