104 research outputs found
Authenticated teleportation with one-sided trust
We introduce a protocol for authenticated teleportation, which can be proven
secure even when the receiver does not trust their measurement devices, and is
experimentally accessible. We use the technique of self-testing from the
device-independent approach to quantum information, where we can characterise
quantum states and measurements from the exhibited classical correlations
alone. First, we derive self-testing bounds for the Bell state and Pauli
measurements, that are robust enough to be implemented in
the lab. Then, we use these to determine a lower bound on the fidelity of an
untested entangled state to be used for teleportation. Finally, we apply our
results to propose an experimentally feasible protocol for one-sided
device-independent authenticated teleportation. This can be interpreted as a
first practical authentication of a quantum channel, with additional one-sided
device-independence.Comment: published versio
Practical sharing of quantum secrets over untrusted channels
In this work we address the issue of sharing a quantum secret over untrusted
channels between the dealer and players. Existing methods require entanglement
over a number of systems which scales with the security parameter, quickly
becoming impractical. We present protocols (interactive and a non-interactive)
where single copy encodings are sufficient. Our protocols work for all quantum
secret sharing schemes and access structures, and are implementable with
current experimental set ups. For a single authorised player, our protocols act
as quantum authentication protocols
Adiabatic graph-state quantum computation
Measurement-based quantum computation (MBQC) and holonomic quantum
computation (HQC) are two very different computational methods. The computation
in MBQC is driven by adaptive measurements executed in a particular order on a
large entangled state. In contrast in HQC the system starts in the ground
subspace of a Hamiltonian which is slowly changed such that a transformation
occurs within the subspace. Following the approach of Bacon and Flammia, we
show that any measurement-based quantum computation on a graph state with
\emph{gflow} can be converted into an adiabatically driven holonomic
computation, which we call \emph{adiabatic graph-state quantum computation}
(AGQC). We then investigate how properties of AGQC relate to the properties of
MBQC, such as computational depth. We identify a trade-off that can be made
between the number of adiabatic steps in AGQC and the norm of as well
as the degree of , in analogy to the trade-off between the number of
measurements and classical post-processing seen in MBQC. Finally the effects of
performing AGQC with orderings that differ from standard MBQC are investigated.Comment: 25 pages, 3 figure
Scheme for constructing graphs associated with stabilizer quantum codes
We propose a systematic scheme for the construction of graphs associated with
binary stabilizer codes. The scheme is characterized by three main steps:
first, the stabilizer code is realized as a codeword-stabilized (CWS) quantum
code; second, the canonical form of the CWS code is uncovered; third, the input
vertices are attached to the graphs. To check the effectiveness of the scheme,
we discuss several graphical constructions of various useful stabilizer codes
characterized by single and multi-qubit encoding operators. In particular, the
error-correcting capabilities of such quantum codes are verified in
graph-theoretic terms as originally advocated by Schlingemann and Werner.
Finally, possible generalizations of our scheme for the graphical construction
of both (stabilizer and nonadditive) nonbinary and continuous-variable quantum
codes are briefly addressed.Comment: 42 pages, 12 figure
Efficient approximate unitary t-designs from partially invertible universal sets and their application to quantum speedup
At its core a -design is a method for sampling from a set of unitaries in
a way which mimics sampling randomly from the Haar measure on the unitary
group, with applications across quantum information processing and physics. We
construct new families of quantum circuits on -qubits giving rise to
-approximate unitary -designs efficiently in
depth. These quantum circuits are based on a relaxation of technical
requirements in previous constructions. In particular, the construction of
circuits which give efficient approximate -designs by Brandao, Harrow, and
Horodecki (F.G.S.L Brandao, A.W Harrow, and M. Horodecki, Commun. Math. Phys.
(2016).) required choosing gates from ensembles which contained inverses for
all elements, and that the entries of the unitaries are algebraic. We reduce
these requirements, to sets that contain elements without inverses in the set,
and non-algebraic entries, which we dub partially invertible universal sets. We
then adapt this circuit construction to the framework of measurement based
quantum computation(MBQC) and give new explicit examples of -qubit graph
states with fixed assignments of measurements (graph gadgets) giving rise to
unitary -designs based on partially invertible universal sets, in a natural
way. We further show that these graph gadgets demonstrate a quantum speedup, up
to standard complexity theoretic conjectures. We provide numerical and
analytical evidence that almost any assignment of fixed measurement angles on
an -qubit cluster state give efficient -designs and demonstrate a quantum
speedup.Comment: 25 pages,7 figures. Comments are welcome. Some typos corrected in
newest version. new References added.Proofs unchanged. Results unchange
Random coding for sharing bosonic quantum secrets
We consider a protocol for sharing quantum states using continuous variable
systems. Specifically we introduce an encoding procedure where bosonic modes in
arbitrary secret states are mixed with several ancillary squeezed modes through
a passive interferometer. We derive simple conditions on the interferometer for
this encoding to define a secret sharing protocol and we prove that they are
satisfied by almost any interferometer. This implies that, if the
interferometer is chosen uniformly at random, the probability that it may not
be used to implement a quantum secret sharing protocol is zero. Furthermore, we
show that the decoding operation can be obtained and implemented efficiently
with a Gaussian unitary using a number of single-mode squeezers that is at most
twice the number of modes of the secret, regardless of the number of players.
We benchmark the quality of the reconstructed state by computing the fidelity
with the secret state as a function of the input squeezing.Comment: Updated figure 1, added figure 2, closer to published versio
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