551 research outputs found
Quantum Key Distribution with Classical Bob
Secure key distribution among two remote parties is impossible when both are
classical, unless some unproven (and arguably unrealistic)
computation-complexity assumptions are made, such as the difficulty of
factorizing large numbers. On the other hand, a secure key distribution is
possible when both parties are quantum.
What is possible when only one party (Alice) is quantum, yet the other (Bob)
has only classical capabilities? We present a protocol with this constraint,
and prove its robustness against attacks: we prove that any attempt of an
adversary to obtain information (and even a tiny amount of information)
necessarily induces some errors that the legitimate users could notice.Comment: 4 and a bit pages, 1 figure, RevTe
Quantum Advantage without Entanglement
We study the advantage of pure-state quantum computation without entanglement
over classical computation. For the Deutsch-Jozsa algorithm we present the
maximal subproblem that can be solved without entanglement, and show that the
algorithm still has an advantage over the classical ones. We further show that
this subproblem is of greater significance, by proving that it contains all the
Boolean functions whose quantum phase-oracle is non-entangling. For Simon's and
Grover's algorithms we provide simple proofs that no non-trivial subproblems
can be solved by these algorithms without entanglement.Comment: 10 page
Signatures of non-classicality in mixed-state quantum computation
We investigate signatures of non-classicality in quantum states, in
particular, those involved in the DQC1 model of mixed-state quantum computation
[Phys. Rev. Lett. 81, 5672 (1998)]. To do so, we consider two known
non-classicality criteria. The first quantifies disturbance of a quantum state
under locally noneffective unitary operations (LNU), which are local unitaries
acting invariantly on a subsystem. The second quantifies measurement induced
disturbance (MID) in the eigenbasis of the reduced density matrices. We study
the role of both figures of non-classicality in the exponential speedup of the
DQC1 model and compare them vis-a-vis the interpretation provided in terms of
quantum discord. In particular, we prove that a non-zero quantum discord
implies a non-zero shift under LNUs. We also use the MID measure to study the
locking of classical correlations [Phys. Rev. Lett. 92, 067902 (2004)] using
two mutually unbiased bases (MUB). We find the MID measure to exactly
correspond to the number of locked bits of correlation. For three or more MUBs,
it predicts the possibility of superior locking effects.Comment: Published version, containing additional discussion on the role of
non-classicality in the locking of classical correlation
Correlation of finite-element structural dynamic analysis with measured free vibration characteristics for a full-scale helicopter fuselage
The correlation achieved with each program provides the material for a discussion of modeling techniques developed for general application to finite-element dynamic analyses of helicopter airframes. Included are the selection of static and dynamic degrees of freedom, cockpit structural modeling, and the extent of flexible-frame modeling in the transmission support region and in the vicinity of large cut-outs. The sensitivity of predicted results to these modeling assumptions are discussed. Both the Sikorsky Finite-Element Airframe Vibration analysis Program (FRAN/Vibration Analysis) and the NASA Structural Analysis Program (NASTRAN) have been correlated with data taken in full-scale vibration tests of a modified CH-53A helicopter
Quantum discord and the power of one qubit
We use quantum discord to characterize the correlations present in the
quantum computational model DQC1, introduced by Knill and Laflamme [Phys. Rev.
Lett. 81, 5672 (1998)]. The model involves a collection of qubits in the
completely mixed state coupled to a single control qubit that has nonzero
purity. The initial state, operations, and measurements in the model all point
to a natural bipartite split between the control qubit and the mixed ones.
Although there is no entanglement between these two parts, we show that the
quantum discord across this split is nonzero for typical instances of the DQC1
ciruit. Nonzero values of discord indicate the presence of nonclassical
correlations. We propose quantum discord as figure of merit for characterizing
the resources present in this computational model.Comment: 4 Pages, 1 Figur
One-Pot Approach for Acoustic Directed Assembly of Metallic and Composite Microstructures by Metal Ion Reduction
Acoustic-directed assembly is a modular and flexible bottom-up technique with
the potential to pattern a wide range of materials. Standing acoustic waves
have been previously employed for patterning preformed metal particles,
however, direct patterning of metallic structures from precursors remains
unexplored. Here, we investigate utilization of standing waves to exert control
over chemical reaction products, while also exploring their potential in the
formation of multi-layered and composite micro-structures. Periodic metallic
micro-structures were formed in a single step, simplifying microstructure
fabrication. Concentric structures were obtained by introducing a metal
precursor salt and a reducing agent into a cylindrical piezoelectric resonator
that also served as a reservoir. In addition, we introduce an innovative
approach to directly fabricate metallic multi-layer and composite structures by
reducing different metal ions or adding nanoparticles during the reduction
step. Fewer steps are needed, compared with other methods, and there is no need
to stabilize the nanoparticles or to ensure chemical affinity between the
metallic matrix and inorganic nanoparticles. This innovative approach is
promising for production of complex microstructures with enhanced functionality
and controlled properties
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