1,357 research outputs found
On the correction of anomalous phase oscillation in entanglement witnesses using quantum neural networks
Entanglement of a quantum system depends upon relative phase in complicated
ways, which no single measurement can reflect. Because of this, entanglement
witnesses are necessarily limited in applicability and/or utility. We propose
here a solution to the problem using quantum neural networks. A quantum system
contains the information of its entanglement; thus, if we are clever, we can
extract that information efficiently. As proof of concept, we show how this can
be done for the case of pure states of a two-qubit system, using an
entanglement indicator corrected for the anomalous phase oscillation. Both the
entanglement indicator and the phase correction are calculated by the quantum
system itself acting as a neural network
A quantum neural network computes its own relative phase
Complete characterization of the state of a quantum system made up of
subsystems requires determination of relative phase, because of interference
effects between the subsystems. For a system of qubits used as a quantum
computer this is especially vital, because the entanglement, which is the basis
for the quantum advantage in computing, depends intricately on phase. We
present here a first step towards that determination, in which we use a
two-qubit quantum system as a quantum neural network, which is trained to
compute and output its own relative phase
Quantum state transfer with untuneable couplings
We present a general scheme for implementing bi-directional quantum state
transfer in a quantum swapping channel. Unlike many other schemes for quantum
computation and communication, our method does not require qubit couplings to
be switched on and off. The only control variable is the bias acting on
individual qubits. We show how to derive the parameters of the system (fixed
and variable) such that perfect state transfer can be achieved. Since these
parameters vary linearly with the pulse width, our scheme allows flexibility in
the time scales under which qubits evolve. Unlike quantum spin networks, our
scheme allows the transmission of several quantum states at a time, requiring
only a two qubit separation between quantum states. By pulsing the biases of
several qubits at the same time, we show that only eight bias control lines are
required to achieve state transfer along a channel of arbitrary length.
Furthermore, when the information to be transferred is purely classical in
nature, only three bias control lines are required, greatly simplifying the
circuit complexity
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