1,720,985 research outputs found
A proposal to measure the Rabi oscillations in the retinal rod cells
No full textStarting from the assumption that rod cells are sensitive to single photons, we propose a method to verify the existence of a quantum superposition in the retina, observing the Rabi oscillations in the quantum interaction of a coherent laser light with the rod cells. The computer simulation shows that the oscillations visibility is a robust parameter, so that it would be possible to observe the fringes also in presence of strong decoherence. The feasibility of the experiment is ensured by the new MEA (microelectrode array) technology, that allows to record the transretinal voltage change of a single retinal segment
Optimal purification of a generic n-qudit state
No full textWe propose a quantum algorithm for the purification of a generic mixed state rho of a n-qudit system by using an ancillary n-qudit system. The algorithm is optimal in that (i) the number of ancillary qudits cannot be reduced, (ii) the number of parameters which determine the purification state | Psi > exactly equals the number of degrees of freedom of rho , and (iii) | Psi > is easily determined from the density matrix rho . Moreover, we introduce a quantum circuit in which the quantum gates are unitary transformations acting on a 2n-qudit system. These transformations are determined by parameters that can be tuned to generate, once the ancillary qudits are disregarded, any given mixed n-qudit state
Simple representation of quantum process tomography
No full textWe show that the Fano representation leads to a particularly simple and appealing form of the quantum
process tomography matrix [chi]F, in that the matrix [chi]F is real, the number of matrix elements is exactly equal to
the number of free parameters required for the complete characterization of a quantum operation, and these
matrix elements are directly related to evolution of the expectation values of the system's polarization measurements.
These facts are illustrated in the examples of one- and two-qubit quantum noise channel
Quantum mechanics in phase space: first order comparison between the Wigner and the Fermi function
No full textThe Fermi gF(x,p) function provides a phase space description of quantum mechanics
conceptually different from that based on the the Wigner function W(x,p).
In this paper, we show that for a peaked wave packet the gF(x,p)=0 curve
approximately corresponds to a phase space contour level of the Wigner function
and provides a satisfactory description of the wave packet's size and shape.
Our results show that the Fermi function is an interesting tool to
investigate quantum fluctuations in the semiclassical regime
Gaussian wave packets in phase space: The Fermi g(F) function
No full textA pure quantum state can be equivalently represented by means of its wave function psi(q) or by the Fermi function g(F)(q,p), with q and p coordinates and conjugate momenta of the system of interest. We show that a Gaussian wave packet can be conveniently visualized in phase space by the curve g(F)(q,p)=0. The change in time of the g(F)=0 curve is calculated for a Gaussian packet evolving freely or under a constant or a harmonic force, and the spreading or shrinking of the packet is easily interpreted in phase space. We also discuss a gedanken prism microscope experiment for measuring the position-momentum correlation. This gedanken experiment, together with the well-known Heisenberg microscope and von Neumann velocimeter, is sufficient to fully determine the state of a Gaussian packet
Quantum noise reduction and instabilities in nondegenerate four-wave mixing
No full textWe start from the exact model for nondegenerate four-wave mixing in a cavity, and derive a relatively simple parametric model. We analyze the oscillatory instabilities and calculate the spectrum of the fluctuations in the intensity difference between the signal and idler fields
Evidences of new biophysical properties of microtubules
No full textMicrotubules (MTs) are cylindrical polymers of the protein tubulin, are key constituents of all eukaryotic cells cytoskeleton and are involved in key cellular functions. Among them MTs are claimed to be involved as sub-cellular information or quantum information communication systems. MTs are the closest biological equivalent to the well known carbon nanotubes (CNTs) material. We evaluated some biophysical properties of MTs through two specific physical measures of resonance and birefringence, on the assumption that when tubulin and MTs show different biophysical behaviours, this should be due to the special structural properties of MTs. The MTs, as well as CNTs, may behave as oscillators, this could make them superreactive receivers able to amplify radio wave signals. Our experimental approach verified the existence of mechanical resonance in MTs at a frequency of 1510 MHz. The analysis of the results of birefringence experiment highlights that the MTs react to electromagnetic fields in a different way than tubulin
Quantum simulation of the single-particle Schrodinger equation
No full textThe nature of a quantum computer is described in the concrete context of a quantum simulator of the single-particle Schrodinger equation. We show that a register of 6-10 qubits is sufficient to realize a useful quantum simulator capable of efficiently solving standard quantum mechanical problem
A single qubit Landau-Zener gate
No full textWe study the hamiltonian and dissipative dynamics of a system undergoing a sequence of level crossings. The resulting Landau-Zener effect makes a new implementation of a general single qubit gate possible. In the dissipative case, with a periodic bias, the level crossing counteracts the interlevel relaxation and drives the system toward a two dimensional attractor. This feature can in principle be used to implement quantum memory devices of new type
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