847 research outputs found
Linearly-independent quantum states can be cloned
A fundamental question in quantum mechanics is, whether it is possible to
replicate an arbitrary unknown quantum state. Then famous quantum no-cloning
theorem [Nature 299, 802 (1982)] says no to the question. But it leaves open
the following question: If the state is not arbitrary, but secretly chosen from
a certain set , whether is the
cloning possible? This question is of great practical significance because of
its applications in quantum information theory. If the states and are linearly-dependent, similar to the proof of
the no-cloning theorem, the linearity of quantum mechanics forbids such
replication. In this paper, we show that, if the states and are linearly-independent, they do can be cloned by a
unitary-reduction process.Comment: 9 pages, no figures, Late
Reply to the comment "quant-ph/9710002"
In the comment, Zanardi and Rasetti argue that several claims in our recent
letter (Phys. Rev. Lett. 79, 1953, 1997) are questionable. The reply shows
these claims remain true.Comment: 2 pages, Late
Decoherence of quantum registers
We consider decoherence of quantum registers, which consist of the qubits
sited approximately periodically in space. The sites of the qubits are
permitted to have a small random variance. We derive the explicit conditions
under which the qubits can be assumed decohering independently. In other
circumstances, the qubits are decohered cooperatively. We describe two kinds of
collective decoherence. In each case, a scheme is proposed for reducing the
collective decoherence. The schemes operate by encoding the input states of the
qubits into some ''subdecoherent'' states.Comment: 12 pages, no figures, Late
Certification of Boson Sampling Devices with Coarse-Grained Measurements
A boson sampling device could efficiently sample from the output probability
distribution of noninteracting bosons undergoing many-body interference. This
problem is not only classically intractable, but its solution is also believed
to be classically unverifiable. Hence, a major difficulty in experiment is to
ensure a boson sampling device performs correctly. We present an experimental
friendly scheme to extract useful and robust information from the quantum boson
samplers based on coarse-grained measurements. The procedure can be applied to
certify the equivalence of boson sampling devices while ruling out alternative
fraudulent devices. We perform numerical simulations to demonstrate the
feasibility of the method and consider the effects of realistic noise. Our
approach is expected to be generally applicable to other many-body
certification tasks beyond the boson sampling problem.Comment: 8 pages including Supplemental Materials, 7 figures, 3 table
Fault Tolerant Quantum Random Number Generator Certified by Majorana Fermions
Braiding of Majorana fermions gives accurate topological quantum operations
that are intrinsically robust to noise and imperfection, providing a natural
method to realize fault-tolerant quantum information processing. Unfortunately,
it is known that braiding of Majorana fermions is not sufficient for
implementation of universal quantum computation. Here we show that topological
manipulation of Majorana fermions provides the full set of operations required
to generate random numbers by way of quantum mechanics and to certify its
genuine randomness through violation of a multipartite Bell inequality. The
result opens a new perspective to apply Majorana fermions for robust generation
of certified random numbers, which has important applications in cryptography
and other related areas.Comment: 4pages of the main text+5 pages of supplementary informatio
Two non-orthogonal states can be cloned by a unitary-reduction process
We show that, there are physical means for cloning two non-orthogonal pure
states which are secretly chosen from a certain set % \$={ | \Psi_0 > , |
\Psi_1 > }. The states are cloned through a unitary evolution together with a
measurement. The cloning efficiency can not attain 100%. With some negative
measurement results, the cloning fails.Comment: 9 pages, no figures, Late
Reducing spatially correlated noise and decoherence with quantum error correcting codes
It is shown that the noise process in quantum computation can be described by
spatially correlated decoherence and dissipation. We demonstrate that the
conventional quantum error correcting codes correcting for single-qubit errors
are applicable for reducing spatially correlated noise.Comment: 8 pages, late
Pulse controlled noise suppressed quantum computation
To make arbitrarily accurate quantum computation possible, practical
realization of quantum computers will require suppressing noise in quantum
memory and gate operations to make it below a threshold value. A scheme based
on realistic quantum computer models is described for suppressing noise in
quantum computation without the cost of stringent quantum computing resources.Comment: 12 pages, late
Cooperative loss and decoherence in quantum computation and commuication
Cooperative effects in the loss (the amplitude damping) and decoherence (the
phase damping) of the qubits (two-state quantum systems) due to the inevitable
coupling to the same environment are investigated. It is found that the qubits
undergo the dissipation coherently in this case. In particular, for a special
kind of input states (called the coherence-preserving states), whose form
depends on the type of the coupling, loss and decoherence in quantum memory are
much reduced. Based on this phenomenon, a scheme by encoding the general input
states of the qubits into the corresponding coherence-preserving states is
proposed for reducing the cooperative loss and decoherence in quantum
computation or communication.Comment: 10 pages, no figures, Late
Quantum Supremacy for Simulating A Translation-Invariant Ising Spin Model
We introduce an intermediate quantum computing model built from
translation-invariant Ising-interacting spins. Despite being non-universal, the
model cannot be classically efficiently simulated unless the polynomial
hierarchy collapses. Equipped with the intrinsic single-instance-hardness
property, a single fixed unitary evolution in our model is sufficient to
produce classically intractable results, compared to several other models that
rely on implementation of an ensemble of different unitaries (instances). We
propose a feasible experimental scheme to implement our Hamiltonian model using
cold atoms trapped in a square optical lattice. We formulate a procedure to
certify the correct functioning of this quantum machine. The certification
requires only a polynomial number of local measurements assuming measurement
imperfections are sufficiently small.Comment: Phys. Rev. Lett.(2017, in press), "one-instance" is replaced by
"single-instance-hardness", references added, "Simulation with variation
Distance Errors" in Supplemental Material is rewritten in a clearer wa
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