Static Quantum Dot Research Articles

Static quantum dot on a large potential hilltop for generating and analyzing hot electrons in the quantum Hall regime

Static quantum dot on a large potential hilltop for generating and analyzing hot electrons in the quantum Hall regime

Lifetime Enhancement of a Circulated Cooling Perovskite Quantum Dots Colloidal Solution System for Laser Illuminations

Perovskite quantum dots (QDs) attracted a lot of attention recently due to their high light conversion efficiency, and high color purity. However, perovskite materials are sensitive to heat. High temperature will cause serious quenching problem of the perovskite QDs. In order to solve the QDs thermal quenching problem without destroying their optical characters. A circulating quantum dots colloidal solution converter (CQD-converter) was developed. A closed loop pump tube coated with Teflon was utilized to prevent perovskite QDs from the external environment. A peristaltic pump was utilized to drive the QDs colloidal solution through a Peltier cooler for dissipating the heat of the QDs colloidal solution. The lifetime of the perovskite QDs can be significantly improved under a 450nm laser excitation. The effects of temperature of the Peltier cooler and flow velocity on the optical properties of QDs were also investigated. Compared to the static quantum dots colloidal solution (SQD-converter), which quenched after 7 min, the optical properties were maintained after 600 min for the CQD-converter.

Transporting and manipulating single electrons in surface‐acoustic‐wave minima

AbstractA surface acoustic wave (SAW) can produce a moving potential wave that can trap and drag electrons along with it. We review work on using a SAW to create moving quantum dots containing single electrons, with the aims of developing a current standard, emitting single photons, transferring single electrons between static quantum dots, and investigating non‐adiabatic effects.

Injection of a single electron from static to moving quantum dots

We study the injection mechanism of a single electron from a static quantum dot into a moving quantum dot. The moving quantum dots are created with surface acoustic waves (SAWs) in a long depleted channel. We demonstrate that the injection process is characterized by an activation law with a threshold that depends on the SAW amplitude and on the dot-channel potential gradient. By sufficiently increasing the SAW modulation amplitude, we can reach a regime where the transfer has unity probability and is potentially adiabatic. This study points to the relevant regime to use moving dots in quantum information protocols.

Entanglement generation due to the Klein tunneling in a graphene sheet

Scattering of a ballistic electron by the quantum-dot spin qubits fixed in a graphene nanoribbon is investigated theoretically. Two simple cases are investigated in details: scattering from a static quantum dot and scattering from two static quantum dots located at a fixed distance from each other. For the first case, it is shown that the Klein tunneling in a graphene sheet leads to a final entangled state for the reflected and/or transmitted electrons. The amount of the generated entanglement through the scattering process is a function of the incident angle for the ballistic electrons. For the second case, it is shown that the created correlation between the quantum dots is a periodic function of their distance. For frontal incident electrons in both cases, there is not any reflection and the Klein tunneling effect leads to a final well-correlated state for the scattering system.

Relaxation of flying spin qubits in quantum wires by hyperfine interaction

We consider the relaxation of a spin qubit in a quantum dot propagating as a whole in a one-dimensional semiconductor with hyperfine coupling. We show that this motion leads to qualitatively new features in this process compared to static quantum dots. For a fast straightforward motion, the initial spin density decreases to zero with the relaxation rate independent of the spatial spread of the electron wave function and inversely proportional to the electron speed. However, for the oscillatory motion, the qubit acquires memory, and the dephasing becomes Gaussian rather than exponential. After some time, one third of the initial spin polarization is restored, as it happens for static qubits. This revival can occur either through periodic peaks or through a monotonous increase in the polarization, after a minimum, until a plateau has been reached. Our results can be useful for the understanding of the spin dynamics and decoherence in quantum wires.

Quantum computation with moving quantum dots generated by surface acoustic waves

Motivated by recent experimental observations [M. Kataoka et al., Phys. Rev. Lett. 102, 156801 (2009)], we propose here a theoretical approach to implement quantum computation with bound states of electrons in moving quantum dots generated by the driving of surface acoustic waves. Differing from static quantum dots defined by a series of static electrodes above the two-dimensional electron gas (2DEG), here a single electron is captured from a 2DEG reservoir by a surface acoustic wave and then trapped in a moving quantum dot (MQD) transported across a quasi-one-dimensional channel, wherein all the electrons have been excluded by the actions of the surface gates. The flying qubit introduced here is encoded by the two lowest levels of the electron in the MQD, and the Rabi oscillation between these two levels could be implemented by applying finely selected microwave pulses to the surface gates. By using the Coulomb interaction between the electrons in different MQDs, we show that a desirable two-qubit operation, i.e., iswap gate, could be realized. Readouts of the present flying qubits are also feasible with the current single-electron detected technique.

Rectification effect for spin- and charge-currents in a shuttled molecule transistor

We have investigated the spin-dependent electronic transports through a shuttled molecule, a molecule self-excitedly oscillating due to suffering an external electric field. When the shuttled molecule is coupled asymmetrically to a ferromagnetic and a normal metal leads, a pronounced dual rectification effect is predicted for both spin- and charge-currents in the Coulomb blockade regime. As compared to the conventional rectifier based on a static quantum dot, the proposed rectifier based on a movable individual molecule has higher rectification efficiency.

Single electron pumping at higher frequency in a novel semiconductor-based quantum dot device

The π-shift sinusoidal signals with different amplitudes applied directly to the two metallic finger gates on a shallow etched GaAs/AlGaAs quantum wire，tune unequally the two barriers of a static quantum dot induced by applying negative dc voltages on these two finger gates. Single electrons are transported through a periodically formed quantum dot without source-drain bias. Since single electron pumping in the novel semiconductor-based quantum dot device does not rely on Coulomb blockade of tunnelling，the device can not be limited to much lower frequency by the fixed tunneling time constant. Current plateaus due to single electron transport can be observed at 1.7K with frequencies up to 3GHz and a current level of 0.5nA. This novel device represents another possible path in the realization of a high current high accuracy quantum standard for electrical current，and also provides another means for high specd high accuracy transport of single electrons.

Generation of Einstein-Podolsky-Rosen pairs and interconversion of static and flying electron spin qubits

We propose a method of generating fully entangled electron spin pairs using an open static quantum dot and a moving quantum dot, realized by the propagation of a surface acoustic wave (SAW) along a quasi-one-dimensional channel in a semiconductor heterostructure. In particular, we consider a static dot (SD) loaded with two interacting electrons in a singlet state and demonstrate a mechanism which enables the moving SAW dot to capture and carry along one of the electrons, hence yielding a fully entangled static-flying pair. We also show how with the same mechanism we can load the SD with one or two electrons which are initially carried by a SAW-induced dot. The feasibility of realizing these ideas with existing semiconductor technology is demonstrated and extended to yield flying or static pairs that are fully entangled and arbitrary interconversion of static and flying electron spin qubits.

Energy-Dependent Tunneling from Few-Electron Dynamic Quantum Dots

We measure the electron escape rate from surface-acoustic-wave dynamic quantum dots (QDs) through a tunnel barrier. Rate equations are used to extract the tunneling rates, which change by an order of magnitude with tunnel-barrier-gate voltage. We find that the tunneling rates depend on the number of electrons in each dynamic QD because of Coulomb energy. By comparing this dependence to a saddle-point-potential model, the addition energies of the second and third electron in each dynamic QD are estimated. The scale ( approximately a few meV) is comparable to those in static QDs as expected.

Quantization of the Current Induced by a Surface Acoustic Wave through a Quantum Point Contact

The acousto-electric currents through a quantum point contact induced by surface acoustic waves were observed. The current was found to be quantized at integer multiples of ef, where f is the surface acoustic frequency. By using an interdigitated transducer with a 500 nm spacing between the gates, we produced surface acoustic waves at 2.456 GHz, which resulted in 1.18 nA quantized current when three electrons were transferred from the source to the drain at a time. Also, we found that the quantization is related to the a presence of a static quantum dot unintentionally formed in a quantum point contact.

Quantized acoustoelectric current transport through a static quantum dot using a surface acoustic wave

We present a detailed study of the surface acoustic wave mediated quantized transport of electrons through a split gate device containing an impurity potential defined quantum dot within the split gate channel. A new regime of quantized transport is observed at low RF powers where the surface acoustic wave amplitude is comparable to the quantum dot charging energy. In this regime resonant transport through the single-electron dot state occurs which we interpret as turnstile-like operation in which the traveling wave amplitude modulates the entrance and exit barriers of the quantum dot in a cyclic fashion at GHz frequencies. For high RF powers, where the amplitude of the surface acoustic wave is much larger than the quantum dot energies, the quantized acoustoelectric current transport shows behavior consistent with previously reported results. However, in this regime, the number of quantized current plateaus observed and the plateau widths are determined by the properties of the quantum dot, demonstrating that the microscopic detail of the potential landscape in the split gate channel has a profound influence on the quantized acoustoelectric current transport.