arXiv subjects

Alexander N. Korotkov

Publications and source records attributed to Alexander N. Korotkov.

101 records · Page 6Linked to original sources

arXiv1999

Continuous quantum measurement of a double dot

We consider the continuous measurement of a double quantum dot by a weakly coupled detector (tunnel point contact nearby). While the conventional approach describes the gradual system decoherence due to the measurement, we study the situation when the detector output is explicitly recorded that leads to the opposite effect: gradual purification of the double-dot density matrix. Nonlinear Langevin equation is derived for the random evolution of the density matrix which is reflected and caused by the stochastic detector output. Gradual collapse, gradual purification, and quantum Zeno effect are naturally described by the equation. We also discuss the possible experiments to confirm the theory.

cond-mat.mes-hall↗

arXiv1999

Density matrix purification due to continuous quantum measurement

We consider the continuous quantum measurement of a two-level system, for example, a single-Cooper-pair box measured by a single-electron transistor or a double-quantum dot measured by a quantum point contact. While the approach most commonly used describes the gradual decoherence of the system due to the measurement, we show that when taking into account the detector output, we get the opposite effect: gradual purification of the density matrix. The competition between purification due to measurement and decoherence due to interaction with the environment can be described by a simple Langevin equation which couples the random evolution of the system density matrix and the stochastic detector output. The gradual density matrix purification due to continuous measurement may be verified experimentally using present-day technology. The effect can be useful for quantum computing.

cond-mat.mes-hall↗

arXiv1999

Possible cooling by resonant Fowler-Nordheim emission

A new method of electronic refrigeration based on resonant Fowler-Nordheim emission is proposed and analyzed. In this method, a bulk emitter is covered with a-few-nm-thick film of a widegap semiconductor, creating an intermediate step between electron energies in the emitter and in vacuum. An external electric field tilts this potential profile, forming a quantum well, and hence 2D electron subbands at the semiconductor-vacuum boundary. Alignment of the lowest subband with the energy levels of the hottest electrons of the emitter (a few $k_{B}T$ above its Fermi level) leads to a resonant, selective emission of these electrons, providing emitter cooling. Calculations show that cooling power as high as 10^{4} W/cm^{2} (at 300 K), and temperatures down to 10 K may be achieved using this effect.

cond-mat.mes-hall↗

arXiv1999

Charge sensitivity of radio frequency single-electron transistor (RF-SET)

A theoretical analysis of the charge sensitivity of the RF-SET is presented. We use the ``orthodox'' approach and consider the case when the carrier frequency is much less than $I/e$ where $I$ is the typical current through RF-SET. The optimized noise-limited sensitivity is determined by the temperature $T$, and at low $T$ it is only 1.4 times less than the sensitivity of conventional single-electron transistor.

cond-mat.mes-hall↗

arXiv1998

Continuous quantum measurement with particular output: pure wavefunction evolution instead of decoherence

We consider a continuous measurement of a two-level system (double-dot) by weakly coupled detector (tunnel point contact nearby). While usual treatment leads to the gradual system decoherence due to the measurement, we show that the knowledge of the measurement result can restore the pure wavefunction at any time (this can be experimentally verified). The formalism allows to write a simple Langevin equation for the random evolution of the system density matrix which is reflected and caused by the stochastic detector output. Gradual wavefunction ``collapse'' and quantum Zeno effect are naturally described by the equation.

quant-ph↗

arXiv1998

Continuous quantum measurement with observer: pure wavefunction evolution instead of decoherence

quant-ph↗

arXiv1998

Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $δ$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $δ$ can become negative.

cond-mat↗

arXiv1997

Quasi-Langevin method for shot noise calculation in single-electron tunneling

It is shown that quasi-Langevin method can be used for the calculation of the shot noise in correlated single-electron tunneling. We generalize the existing Fokker-Plank-type approach and show its equivalence to quasi-Langevin approach. The advantage of the quasi-Langevin method is a natural possibility to describe simultaneously the high (``quantum'') frequency range.

cond-mat.str-el↗

arXiv1996

Charge Sensitivity of Superconducting Single-Electron Transistor

It is shown that the noise-limited charge sensitivity of a single-electron transistor using superconductors (of either $SISIS$ or $NISIN$ type) operating near the threshold of quasiparticle tunneling, can be considerably higher than that of a similar transistor made of normal metals or semiconductors. The reason is that the superconducting energy gap, in contrast to the Coulomb blockade, is not smeared by the finite temperature. We discuss also the increase of the maximum operation temperature due to superconductivity and a new peak-like feature on the $I-V$ curve of $SISIS$ structures.

cond-mat↗

arXiv1996

Coulomb Blockade and Digital Single-Electron Devices

Tunneling of single electrons has been thoroughly studied both theoretically and experimentally during last ten years. By the present time the basic physics is well understood, and creation of useful single-electron devices becomes the important issue. Single-electron tunneling seems to be the most promising candidate to be used in the future integrated digital circuits with the typical size scale of few nanometers and below, i.e. in the molecular electronics. In the review we first briefly discuss the physics of single-electron tunneling and the operation of the single-electron transistor. After that, we concentrate on the hypothetical ultradense digital single-electron circuits and discuss the different proposed families of them. The last part of the review considers the issues of the discrete energy spectrum and the finite tunnel barrier height which are important for the molecular-size single-electron devices.

cond-mat↗

arXiv1996

Single-Electron Parametron: Reversible Computation in a Discrete State System

We have analyzed energy dissipation in a digital device (``Single-Electron Parametron'') in which discrete degrees of freedom are used for presenting digital information. If the switching speed is not too high, the device may operate reversibly (adiabatically), and the energy dissipation ${\cal E}$ per bit may be much less than the thermal energy $k_BT$. The energy-time product ${\cal E}τ$ is, however, much larger than Planck's constant $\hbar $, at least in the standard ``orthodox'' model of single-electron tunneling, which was used in our calculations.

cond-mat↗