4,451 research outputs found
Exact Boson Sampling using Gaussian continuous variable measurements
BosonSampling is a quantum mechanical task involving Fock basis state
preparation and detection and evolution using only linear interactions. A
classical algorithm for producing samples from this quantum task cannot be
efficient unless the polynomial hierarchy of complexity classes collapses, a
situation believe to be highly implausible. We present method for constructing
a device which uses Fock state preparations, linear interactions and Gaussian
continuous-variable measurements for which one can show exact sampling would be
hard for a classical algorithm in the same way as Boson Sampling. The detection
events used from this arrangement does not allow a similar conclusion for the
classical hardness of approximate sampling to be drawn. We discuss the details
of this result outlining some specific properties that approximate sampling
hardness requires
Boson Sampling from Gaussian States
We pose a generalized Boson Sampling problem. Strong evidence exists that
such a problem becomes intractable on a classical computer as a function of the
number of Bosons. We describe a quantum optical processor that can solve this
problem efficiently based on Gaussian input states, a linear optical network
and non-adaptive photon counting measurements. All the elements required to
build such a processor currently exist. The demonstration of such a device
would provide the first empirical evidence that quantum computers can indeed
outperform classical computers and could lead to applications
Language-independent model transformation verification
One hinderance to model transformation verification is the large number of different MT languages which exist, resulting in a large number of different language-specific analysis tools. As an alternative, we define a single analysis process which can, in principle, analyse speci- fications in several different transformation languages, by making use of a common intermediate representation to express the semantics of trans- formations in any of these languages. Some analyses can be performed directly on the intermediate representation, and further semantic models in specific verification formalisms can be derived from it. We illustrate the approach by applying it to ATL
On the feasibility of attribute-based encryption on Internet of Things devices
Attribute-based encryption (ABE) could be an effective cryptographic tool for the secure management of Internet of Things (IoT) devices, but its feasibility in the IoT has been under-investigated thus far. This article explores such feasibility for well-known IoT platforms, namely, Intel Galileo Gen 2, Intel Edison, Raspberry pi 1 model B, and Raspberry pi zero, and concludes that adopting ABE in the IoT is indeed feasible
Coherent back-scattering near the two-dimensional metal-insulator transition
We have studied corrections to conductivity due to the coherent
backscattering in low-disordered two-dimensional electron systems in silicon
for a range of electron densities including the vicinity of the metal-insulator
transition, where the dramatic increase of the spin susceptibility has been
observed earlier. We show that the corrections, which exist deeper in the
metallic phase, weaken upon approaching to the transition and practically
vanish at the critical density, thus suggesting that the localization is
suppressed near and at the transition even in zero field.Comment: to appear in PR
Quantum process tomography with coherent states
We develop an enhanced technique for characterizing quantum optical processes
based on probing unknown quantum processes only with coherent states. Our
method substantially improves the original proposal [M. Lobino et al., Science
322, 563 (2008)], which uses a filtered Glauber-Sudarshan decomposition to
determine the effect of the process on an arbitrary state. We introduce a new
relation between the action of a general quantum process on coherent state
inputs and its action on an arbitrary quantum state. This relation eliminates
the need to invoke the Glauber-Sudarshan representation for states; hence it
dramatically simplifies the task of process identification and removes a
potential source of error. The new relation also enables straightforward
extensions of the method to multi-mode and non-trace-preserving processes. We
illustrate our formalism with several examples, in which we derive analytic
representations of several fundamental quantum optical processes in the Fock
basis. In particular, we introduce photon-number cutoff as a reasonable
physical resource limitation and address resource vs accuracy trade-off in
practical applications. We show that the accuracy of process estimation scales
inversely with the square root of photon-number cutoff.Comment: 18 pages, 2 figure
Reducing Drift in Parametric Motion Tracking
We develop a class of differential motion trackers that automatically stabilize when in finite domains. Most differ-ential trackers compute motion only relative to one previous frame, accumulating errors indefinitely. We estimate pose changes between a set of past frames, and develop a probabilistic framework for integrating those estimates. We use an approximation to the posterior distribution of pose changes as an uncertainty model for parametric motion in order to help arbitrate the use of multiple base frames. We demonstrate this framework on a simple 2D translational tracker and a 3D, 6-degree of freedom tracker
Spin-independent origin of the strongly enhanced effective mass in a dilute 2D electron system
We have accurately measured the effective mass in a dilute two-dimensional
electron system in silicon by analyzing temperature dependence of the
Shubnikov-de Haas oscillations in the low-temperature limit. A sharp increase
of the effective mass with decreasing electron density has been observed. Using
tilted magnetic fields, we have found that the enhanced effective mass is
independent of the degree of spin polarization, which points to a
spin-independent origin of the mass enhancement and is in contradiction with
existing theories
Development of microstructure and crystallographic texture in a double-sided friction stir welded microalloyed steel
The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the centre of stirred zone reached a temperature between Ac1 – Ac3 during FSW, resulting in a dual phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool, show the dominance of simple shear components across the whole weld. The austenite texture at Ac1 – Ac3 is dominated by the B{11 ̅2} and ¯B {1 ̅12 ̅ } simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1{1 ̅1 ̅2} and D2{112 ̅ } simple shear texture components. The formation of ultra-fine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallisation as a result of simultaneous severe shear deformation and drastic undercooling
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