688 research outputs found
Thermodynamic cost of reversible computing
Since reversible computing requires preservation of all information
throughout the entire computational process, this implies that all errors that
appear as a result of the interaction of the information-carrying system with
uncontrolled degrees of freedom must be corrected. But this can only be done at
the expense of an increase in the entropy of the environment corresponding to
the dissipation, in the form of heat, of the ``noisy'' part of the system's
energy.
This paper gives an expression of that energy in terms of the effective noise
temperature, and analyzes the relationship between the energy dissipation rate
and the rate of computation. Finally, a generalized Clausius principle based on
the concept of effective temperature is presented.Comment: 5 pages; added two paragraphs and fixed a number of typo
The fundamental limit on the rate of quantum dynamics: the unified bound is tight
The question of how fast a quantum state can evolve has attracted a
considerable attention in connection with quantum measurement, metrology, and
information processing. Since only orthogonal states can be unambiguously
distinguished, a transition from a state to an orthogonal one can be taken as
the elementary step of a computational process. Therefore, such a transition
can be interpreted as the operation of "flipping a qubit", and the number of
orthogonal states visited by the system per unit time can be viewed as the
maximum rate of operation.
A lower bound on the orthogonalization time, based on the energy spread
DeltaE, was found by Mandelstam and Tamm. Another bound, based on the average
energy E, was established by Margolus and Levitin. The bounds coincide, and can
be exactly attained by certain initial states if DeltaE=E; however, the problem
remained open of what the situation is otherwise.
Here we consider the unified bound that takes into account both DeltaE and E.
We prove that there exist no initial states that saturate the bound if DeltaE
is not equal to E. However, the bound remains tight: for any given values of
DeltaE and E, there exists a one-parameter family of initial states that can
approach the bound arbitrarily close when the parameter approaches its limit
value. The relation between the largest energy level, the average energy, and
the orthogonalization time is also discussed. These results establish the
fundamental quantum limit on the rate of operation of any
information-processing system.Comment: 4 pages 1 PS figure Late
Enhanced Resolution of Lossy Interferometry by Coherent Amplification of Single Photons
In the quantum sensing context most of the efforts to design novel quantum
techniques of sensing have been constrained to idealized, noise-free scenarios,
in which effects of environmental disturbances could be neglected. In this
work, we propose to exploit optical parametric amplification to boost
interferometry sensitivity in the presence of losses in a minimally invasive
scenario. By performing the amplification process on the microscopic probe
after the interaction with the sample, we can beat the losses detrimental
effect on the phase measurement which affects the single-photon state after its
interaction with the sample, and thus improve the achievable sensitivity.Comment: 4 + 3 pages, 3 + 5 figure
Quantum to classical transition via fuzzy measurements on high gain spontaneous parametric down-conversion
We consider the high gain spontaneous parametric down-conversion in a non
collinear geometry as a paradigmatic scenario to investigate the
quantum-to-classical transition by increasing the pump power, that is, the
average number of generated photons. The possibility of observing quantum
correlations in such macroscopic quantum system through dichotomic measurement
will be analyzed by addressing two different measurement schemes, based on
different dichotomization processes. More specifically, we will investigate the
persistence of non-locality in an increasing size n/2-spin singlet state by
studying the change in the correlations form as increases, both in the
ideal case and in presence of losses. We observe a fast decrease in the amount
of Bell's inequality violation for increasing system size. This theoretical
analysis is supported by the experimental observation of macro-macro
correlations with an average number of photons of about 10^3. Our results
enlighten the practical extreme difficulty of observing non-locality by
performing such a dichotomic fuzzy measurement.Comment: 15 pages, 18 figure
The biochemical basis of interactions between Glucocerebrosidase and alphaâsynuclein in GBA1 mutation carriers
The discovery of genes involved in familial as well as sporadic forms of Parkinson disease (PD) constitutes an important milestone in understanding this disorder's pathophysiology and potential treatment. Among these genes, GBA1 is one of the most common and well-studied, but it is still unclear how mutations in GBA1 translate into an increased risk for developing PD. In this review, we provide an overview of the biochemical and structural relationship between GBA1 and PD to help understand the recent advances in the development of PD therapies intended to target this pathway
Modulational instability and wave amplification in finite water depth
The modulational instability of a uniform wave train to side band
perturbations is one of the most plausible mechanisms for the generation of
rogue waves in deep water. In a condition of finite water depth, however, the
interaction with the sea floor generates a wave-induced current that
subtracts energy from the wave field and consequently attenuates the
instability mechanism. As a result, a plane wave remains stable under the
influence of collinear side bands for relative depths <i>kh</i> ≤ 1.36 (where <i>k</i>
is the wavenumber of the plane wave and <i>h</i> is the water depth), but it can
still destabilise due to oblique perturbations. Using direct numerical
simulations of the Euler equations, it is here demonstrated that oblique side
bands are capable of triggering modulational instability and eventually
leading to the formation of rogue waves also for <i>kh</i> ≤ 1.36. Results,
nonetheless, indicate that modulational instability cannot sustain a
substantial wave growth for <i>kh</i> < 0.8
Three-Qubit Gate Realization Using Single Quantum Particle
Using virtual spin formalism it is shown that a quantum particle with eight
energy levels can store three qubits. The formalism allows to realize a
universal set of quantum gates. Feasible formalism implementation is suggested
which uses nuclear spin-7/2 as a storage medium and radio frequency pulses as
the gates. One pulse realization of all universal gates has been found,
including three-qubit Toffoli gate.Comment: LaTeX, 6 pages, no figures; Submitted to "Pis'ma v Zh. Eksp. Teor.
Fiz.
Current Trends in Urinary Diversion in Men
Prior to the introduction of the ileal conduit more than four decades ago, the options for
urinary diversion after cystectomy were extremely limited. Direct cutaneous anastomoses of
the collecting system (cutaneous pyelostomies, ureterostomies) offered patients a short-term
diversion, but the benefits were outweighed by significant complications: recession or
stenosis of the stoma. The first choice of diversion was the ureterosigmoidostomy with or
without antireflux technique. Then it fell in popularity and was replaced with
continent/non-continent uretero-ileo-cutaneous diversions. Only in the last years the
continent orthotopic neobladder has been widely employed as first procedure choice. At
present, patients can be offered a non-continent cutaneous diversion, a continent cutaneous
diversion or an orthotopic neobladder urinary reconstructio
Rogue waves in opposite currents: an experimental study on deterministic and stochastic wave trains
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