Adiabatic Pumping Research Articles

Cyclotron-resonance maser with adiabatic magnetic pumping in a low-density plasma

The conditions under which the magnetic adiabatic compression of a plasma in a direct magnetic trap is accompanied by the accumulation of high energy in the hot anisotropic electron component are found. The basic instabilities resulting in the emission of the accumulated energy in the form of a pulse of stimulated electromagnetic radiation are analyzed. The possibility of creating terahertz radiation sources with the use of the magnetic compression of the plasma is discussed.

Adiabatic Quantum Pumping at the Josephson Frequency

We analyze theoretically adiabatic quantum pumping through a normal conductor that couples the normal regions of two superconductor - normal-metal - superconductor Josephson junctions. By using the phases of the superconducting order parameter in the superconducting contacts as pumping parameters, we demonstrate that a nonzero pumped charge can flow through the device. The device exploits the evolution of the superconducting phases due to the ac Josephson effect, and can therefore be operated at very high frequency, resulting in a pumped current as large as a few nanoamperes. The experimental relevance of our calculations is discussed.

Adiabatic quantum pumping in an Aharonov-Bohm loop and in a siliconlike nanowire: The role of interference in position space and in momentum space

We study the consequences of interference effects on the current generated by adiabatic quantum pumping in two distinct one-dimensional lattice models. The first model contains an Aharonov-Bohm (AB) loop within a tight-binding chain of lattice sites. The static AB phase is shown to strongly affect interference between the two arms of the loop, serving as an on-off switch and regulator for the pumped current. The second model simulates pumping in semiconductors with indirect band gaps by utilizing a tight-binding chain with next-nearest-neighbor coupling. The model exhibits signatures of interference between degenerate conduction band states with different Fermi wave vectors.

Quantum charge pumping and electric polarization in Anderson insulators

We investigate adiabatic charge pumping in disordered system in one dimension with open and closed boundary conditions. In contrast to the Thouless charge pumping, the system has no gap even though all the states are localized, i.e., strong localization. Charge pumping can be achieved by making a loop adiabatically in the two-dimensional parameter space of the Hamiltonian. It is because there are many $\delta$-function-like fluxes distributed over the parameter space with random strength, in sharp contrast to the single $\delta$-function in the pure case. This provides a new and more efficient way of charge pumping and polarization.

A Novel Charge Recycling Design Scheme Based on Adiabatic Charge Pump

Power consumption has become a critical design criterion for integrated circuits given the growing importance of portable battery-operated devices. A typical CMOS gate driven by power supply (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> ), draws energy equal to C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> during every cycle of operation. We propose a new approach to recycle the charge with an adiabatic charge pump that moves the slower adiabatic components away from the critical path of logic. The critical path of the system, and hence the delay, do not change. This is achieved by overlapping the adiabatic charge pump delays with the computing path logic delays. Many embedded high performance applications such as digital signal processing (DSP), which exhibit datapath parallelism, are ideal candidates for this scheme. The proposed method has been implemented in DSP computations. SPICE simulations-based results indicate that the proposed scheme reduces energy consumption in these DSP circuits by as much as 18% (on average 9.94%) with no perceptible loss in performance. The area penalty for these energy savings are in the 1%-2% range, The leakage energy reduction in 45-nm BPTM averages 46%.

Pumping through a quantum dot in the proximity of a superconductor

We study adiabatic pumping through a quantum dot tunnel coupled to one normal and one superconducting lead. We generalize a formula which relates the pumped charge through a quantum dot with Coulomb interaction to the instantaneous local Green's function of the dot, to systems containing a superconducting lead. First, we apply this formula to the case of a noninteracting, single-level quantum dot in different temperature regimes and for different parameter choices, and we compare the results with the case of a system comprising only normal leads. Then we study the infinite-$U$ Anderson model with a superconducting lead at zero temperature, and we discuss the effect of the proximity of the superconductor on the pumped charge.

Quantum pump driven fermionic Mach-Zehnder interferometer

We have investigated the characteristics of the currents in a pump-driven fermionic Mach-Zehnder interferometer. The system is implemented in a conductor in the quantum Hall regime, with the two interferometer arms enclosing an Aharonov-Bohm flux $\Phi$. Two quantum point contacts with transparency modulated periodically in time drive the current and act as beam-splitters. The current has a flux dependent part $I^{(\Phi)}$ as well as a flux independent part $I^{(0)}$. Both current parts show oscillations as a function of frequency on the two scales determined by the lengths of the interferometer arms. In the non-adiabatic, high frequency regime $I^{(\Phi)}$ oscillates with a constant amplitude while the amplitude of the oscillations of $I^{(0)}$ increases linearly with frequency. The flux independent part $I^{(0)}$ is insensitive to temperature while the flux dependent part $I^{(\Phi)}$ is exponentially suppressed with increasing temperature. We also find that for low amplitude, adiabatic pumping rectification effects are absent for semitransparent beam-splitters. Inelastic dephasing is introduced by coupling one of the interferometer arms to a voltage probe. For a long charge relaxation time of the voltage probe, giving a constant probe potential, $I^{(\Phi)}$ and the part of $I^{(0)}$ flowing in the arm connected to the probe are suppressed with increased coupling to the probe. For a short relaxation time, with the potential of the probe adjusting instantaneously to give zero time dependent current at the probe, only $I^{(\Phi)}$ is suppressed by the coupling to the probe.

Time-resolved noise of adiabatic quantum pumps

We investigate quantum-statistical correlation properties of a periodically driven mesoscopic scatterer on a time scale shorter than the period of a drive. In this limit the intrinsic quantum fluctuations in the system of fermions are the main source of a noise. Nevertheless the effect of a slow periodic drive is clearly visible in a two-time current-current correlation function as a specific periodic in time modulation. In the limit of a strong drive such a modulation can change the sign of a current correlation function.

Spin pumping with quantum dots

The purpose of this paper is to discuss how lateral semiconductor quantum dots can be used as pumps to produce spin polarised currents, by exploring quantum phase coherence phenomena. Electronic transport in phase coherent or mesoscopic systems has been intensively studied for more than three decades. While there is a substantial understanding of the stationary regime, much less is known about phase-coherent non-equilibrium transport when pulses or ac perturbations are used to drive electrons at low temperatures and at small length scales. However, about 20 years ago Thouless proposed to drive non-dissipative currents in quantum systems by applying simultaneously two phase-locked external perturbations. The so-called adiabatic pumping mechanism has been revived in the last few years, both theoretically and experimentally, in part because of the development of lateral semiconductor quantum dots. Here we show how open dots can be used to create spin-polarised currents with little or no net charge transfer. The pure spin pump we propose is the analog of a charge battery in conventional electronics and may provide a needed circuit element for spin-based electronics. We also briefly discuss other relevant issues such as rectification and decoherence and point out possible extensions of the pumping mechanism to closed quantum dots.

Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping

We propose a method to dynamically generate and control the flow of spin-entangled electrons, each belonging to a spin singlet, by means of adiabatic quantum pumping. The pumping cycle functions by periodic time variation of localized two-body interactions. We develop a generalized approach to adiabatic quantum pumping as traditional methods based on a scattering matrix in one dimension cannot be applied here. We specifically compute the flow of spin-entangled electrons within a Hubbard-like model of quantum dots, discuss possible implementations, and identify parameters that can be used to control the singlet flow.

Adiabatic pumping through a quantum dot with coulomb interactions: A perturbation expansion in the tunnel coupling

We present a diagrammatic real-time approach to adiabatic pumping of electrons through interacting quantum dots. Performing a systematic perturbation expansion in the tunnel-coupling strength, we compute the charge pumped through a single-level quantum dot per pumping cycle. The combination of coulomb interaction and quantum fluctuations, accounted for in contributions of higher order in the tunnel coupling, modifies the pumping characteristics via an interaction-dependent renormalization of the quantum-dot level. The latter is even responsible for the dominant contribution to the pumped charge when pumping via time-dependent tunnel-coupling strengths.

Measurement scheme of the Berry phase in superconducting circuits

We present a measurement scheme for observing the Berry phase in a flux assisted Cooper pair pump - the Cooper pair sluice. In contrast to the recent experiments, in which the sluice was employed to generate accurate current through a resistance, we consider a device in a superconducting loop. This arrangement introduces a connection between the pumped current and the Berry phase accumulated during the adiabatic pumping cycles. From the adiabaticity criterion, we derive equations for the maximum pumped current and optimize the sluice accordingly. These results apply also to the high accuracy pumping which results in a potential candidate for a metrological current standard. For measuring the pumped current, an additional Josephson junction is installed into the superconducting loop. We show in detail that the switching of this system from superconducting state into normal state as a consequence of an external current pulse through it may be employed to probe the pumped current. The experimental realization of our scheme would be the first observation of the Berry phase in superconducting circuits.

Adiabatic Pumping in Interacting Systems

A dc current can be pumped through an interacting system by periodically varying two independent parameters such as the magnetic field and a gate potential. We present a general expression for the adiabatic pumping current in interacting systems, written in terms of instantaneous properties of the system at equilibrium, and find the limits of its applicability. This expression generalizes the scattering approach for noninteracting particles. We apply our formula for a quantum critical system that exhibits the two-channel Kondo effect, where single particle excitations are not well defined. We find that if the quantum critical point is contained in the pumping trajectory, the pumped spin between the channels approaches h, and if it is not contained in the trajectory, the spin approaches zero when the temperature T --> 0. We discuss the non-Fermi liquid features of this system at finite T.

Pure spin currents generation in magnetic tunnel junctions by means of adiabatic quantum pumping

We study the spin polarized currents generation in a magnetic (ferromagnetic/ferromagnetic) tunnel junction by means of adiabatic quantum pumping. Using a scattering matrix approach, it is shown that a pure spin current can be pumped from one ferromagnetic lead into the adjacent one by adiabatic modulation of the magnetization and the height of the barrier at the interface in absence of external bias voltage. We numerically study the characteristic features of the pure spin current and discuss its behavior for realistic values of the parameters. We show that the generated pure spin current is robust with respect to the variation of the magnetization strength, a very important feature for a realistic device, and that the proposed device can operate close to the optimal pumping regime. An experimental realization of a pure spin current injector is also discussed.

Operating a quantum pump in a closed circuit

During an adiabatic pumping cycle a conventional two barrier quantum device takes an electron from the left lead and ejects it to the right lead. Hence the pumped charge per cycle is naively expected to be $Q \le e$. This zero order adiabatic point of view is in fact misleading. For a closed device we can get ${Q > e}$ and even ${Q \gg e}$. In this paper a detailed analysis of the quantum pump operation is presented. Using the Kubo formula for the geometric conductance, and applying the Dirac chains picture, we derive practical estimates for~$Q$.

Adiabatic quantum pumping of a desired ratio of spin current to charge current

We present a prescription for generating a pure spin current or spin selective current, based on adiabatic quantum pumping in a tight-binding model of a one-dimensional conductor. A formula for the instantaneous pumped current is derived without introducing the scattering matrix. Our calculations indicate that some pumping cycles produce the maximum value 2 of pumped spin while others reverse the direction of current as a result of small alterations of the pumping cycle. We find pumping cycles which produce essentially any ratio of spin current to charge current.

Nonlinear tuning of 3D photonic band-gap structures for single-photon on demand sources

We describe a practical implementation of a semi-deterministic photon gun based on the stimulated Raman adiabatic passage pumping and the nonlinear tuning of the photonic density of states in a photonic band-gap material. We show that this device allows deterministic and unidirectional production of single photons with a high repetition rate of the order of 100 kHz. We also discuss specific 3D photonic microstructure architectures in which our model can be realized and the feasibility of implementing such a device using Er 3 + ions that produce single photons at the telecommunication wavelength of 1.55 μ m .

Adiabatic Pumping in a Superconductor-Normal-Superconductor Weak Link

We present a formalism to study adiabatic pumping through a superconductor-normal-superconductor weak link. At zero temperature, the pumped charge is related to the Berry phase accumulated, in a pumping cycle, by the Andreev bound states. We analyze in detail the case when the normal region is short compared to the superconducting coherence length. The pumped charge turns out to be an even function of the superconducting phase difference. Hence, it can be distinguished from the charge transferred due to the standard Josephson effect.

Adiabatic Pumping through Interacting Quantum Dots

We present a general formalism to study adiabatic pumping through interacting quantum dots. We derive a formula that relates the pumped charge to the local, instantaneous Green's function of the dot. This formula is then applied to the infinite-U Anderson model for both weak and strong tunnel-coupling strengths.

Nonlocal pure spin current injection via quantum pumping and crossed Andreev reflection

A pure spin current injector is proposed based on adiabatic pumping and crossed normal and Andreev reflection. The device consists of a three-terminal ferromagnet-superconductor-semiconductor system in which the injection of a pure spin current is into the semiconductor which is coupled to the superconductor within a coherence length away from the ferromagnet enabling the phenomena of crossed normal/Andreev reflection to operate. Quantum pumping is induced by adiabatically modulating two independent parameters of the ferromagnetic lead, namely, the magnetization strength and the strength of coupling between the ferromagnet and the superconductor. The competition between the normal/Andreev reflection and the crossed normal/Andreev reflection, both induced by pumping, leads to nonlocal injection of a pure spin current into the semiconductor. The experimental realization of the proposed device is also discussed.