5,937 research outputs found
On Burst Error Correction and Storage Security of Noisy Data
Secure storage of noisy data for authentication purposes usually involves the
use of error correcting codes. We propose a new model scenario involving burst
errors and present for that several constructions.Comment: to be presented at MTNS 201
Stabilisation of Quantum Computations by Symmetrisation
We propose a method for the stabilisation of quantum computations (including
quantum state storage). The method is based on the operation of projection into
, the symmetric subspace of the full state space of redundant
copies of the computer. We describe an efficient algorithm and quantum network
effecting --projection and discuss the stabilising effect of the
proposed method in the context of unitary errors generated by hardware
imprecision, and nonunitary errors arising from external environmental
interaction. Finally, limitations of the method are discussed.Comment: 20 pages LaTeX, 2 postscript figure
Universal blind quantum computation
We present a protocol which allows a client to have a server carry out a
quantum computation for her such that the client's inputs, outputs and
computation remain perfectly private, and where she does not require any
quantum computational power or memory. The client only needs to be able to
prepare single qubits randomly chosen from a finite set and send them to the
server, who has the balance of the required quantum computational resources.
Our protocol is interactive: after the initial preparation of quantum states,
the client and server use two-way classical communication which enables the
client to drive the computation, giving single-qubit measurement instructions
to the server, depending on previous measurement outcomes. Our protocol works
for inputs and outputs that are either classical or quantum. We give an
authentication protocol that allows the client to detect an interfering server;
our scheme can also be made fault-tolerant.
We also generalize our result to the setting of a purely classical client who
communicates classically with two non-communicating entangled servers, in order
to perform a blind quantum computation. By incorporating the authentication
protocol, we show that any problem in BQP has an entangled two-prover
interactive proof with a purely classical verifier.
Our protocol is the first universal scheme which detects a cheating server,
as well as the first protocol which does not require any quantum computation
whatsoever on the client's side. The novelty of our approach is in using the
unique features of measurement-based quantum computing which allows us to
clearly distinguish between the quantum and classical aspects of a quantum
computation.Comment: 20 pages, 7 figures. This version contains detailed proofs of
authentication and fault tolerance. It also contains protocols for quantum
inputs and outputs and appendices not available in the published versio
Glory Oscillations in the Index of Refraction for Matter-Waves
We have measured the index of refraction for sodium de Broglie waves in gases
of Ar, Kr, Xe, and nitrogen over a wide range of sodium velocities. We observe
glory oscillations -- a velocity-dependent oscillation in the forward
scattering amplitude. An atom interferometer was used to observe glory
oscillations in the phase shift caused by the collision, which are larger than
glory oscillations observed in the cross section. The glory oscillations depend
sensitively on the shape of the interatomic potential, allowing us to
discriminate among various predictions for these potentials, none of which
completely agrees with our measurements
Unconditionally verifiable blind computation
Blind Quantum Computing (BQC) allows a client to have a server carry out a
quantum computation for them such that the client's input, output and
computation remain private. A desirable property for any BQC protocol is
verification, whereby the client can verify with high probability whether the
server has followed the instructions of the protocol, or if there has been some
deviation resulting in a corrupted output state. A verifiable BQC protocol can
be viewed as an interactive proof system leading to consequences for complexity
theory. The authors, together with Broadbent, previously proposed a universal
and unconditionally secure BQC scheme where the client only needs to be able to
prepare single qubits in separable states randomly chosen from a finite set and
send them to the server, who has the balance of the required quantum
computational resources. In this paper we extend that protocol with new
functionality allowing blind computational basis measurements, which we use to
construct a new verifiable BQC protocol based on a new class of resource
states. We rigorously prove that the probability of failing to detect an
incorrect output is exponentially small in a security parameter, while resource
overhead remains polynomial in this parameter. The new resource state allows
entangling gates to be performed between arbitrary pairs of logical qubits with
only constant overhead. This is a significant improvement on the original
scheme, which required that all computations to be performed must first be put
into a nearest neighbour form, incurring linear overhead in the number of
qubits. Such an improvement has important consequences for efficiency and
fault-tolerance thresholds.Comment: 46 pages, 10 figures. Additional protocol added which allows
arbitrary circuits to be verified with polynomial securit
Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-delay Polarization Modulators
Variable-delay Polarization Modulators (VPMs) are currently being implemented
in experiments designed to measure the polarization of the cosmic microwave
background on large angular scales because of their capability for providing
rapid, front-end polarization modulation and control over systematic errors.
Despite the advantages provided by the VPM, it is important to identify and
mitigate any time-varying effects that leak into the synchronously modulated
component of the signal. In this paper, the effect of emission from a K
VPM on the system performance is considered and addressed. Though instrument
design can greatly reduce the influence of modulated VPM emission, some
residual modulated signal is expected. VPM emission is treated in the presence
of rotational misalignments and temperature variation. Simulations of
time-ordered data are used to evaluate the effect of these residual errors on
the power spectrum. The analysis and modeling in this paper guides
experimentalists on the critical aspects of observations using VPMs as
front-end modulators. By implementing the characterizations and controls as
described, front-end VPM modulation can be very powerful for mitigating
noise in large angular scale polarimetric surveys. None of the systematic
errors studied fundamentally limit the detection and characterization of
B-modes on large scales for a tensor-to-scalar ratio of . Indeed,
is achievable with commensurately improved characterizations and
controls.Comment: 13 pages, 13 figures, 1 table, matches published versio
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