30 research outputs found
Surface Acoustic Wave Single-Electron Interferometry
We propose an experiment to observe interference of a single electron as it
is transported along two parallel quasi-one-dimensional channels trapped in a
single minimum of a travelling periodic electric field. The experimental device
is a modification of the surface acoustic wave (SAW) based quantum processor.
Interference is achieved by creating a superposition of spatial wavefunctions
between the two channels and inducing a relative phase shift via either a
transverse electric field or a magnetic field. The interference can be used to
estimate the decoherence time of an electron in this type of solid-state
device
Charge Pumping in Carbon Nanotubes
We demonstrate charge pumping in semiconducting carbon nanotubes by a
traveling potential wave. From the observation of pumping in the nanotube
insulating state we deduce that transport occurs by packets of charge being
carried along by the wave. By tuning the potential of a side gate, transport of
either electron or hole packets can be realized. Prospects for the realization
of nanotube based single-electron pumps are discussed
Acoustoelectric current and pumping in a ballistic quantum point contact
The acoustoelectric current induced by a surface acoustic wave (SAW) in a
ballistic quantum point contact is considered using a quantum approach. We find
that the current is of the "pumping" type and is not related to drag, i.e. to
the momentum transfer from the wave to the electron gas. At gate voltages
corresponding to the plateaus of the quantized conductance the current is
small. It is peaked at the conductance step voltages. The peak current
oscillates and decays with increasing SAW wavenumber for short wavelengths.
These results contradict previous calculations, based on the classical
Boltzmann equation.Comment: 4 pages, 1 figur
Transport of a Luttinger liquid in the presence of a time dependent impurity
We show that the macroscopic current and charge can be formulated as a
Quantum Mechanical zero mode problem. We find that the current is given by the
velocity operator of a particle restricted to move around a circle. As an
explicit example we investigate a Luttinger liquid of length which is
perturbed by a time dependent impurity. Using the statistical mechanics of zero
modes we computed the non-equilibrium current. In particular we show that in
the low temperature limit, , the zero mode method introduced here
becomes essential for computing the current
Non-adiabaticity and single-electron transport driven by surface acoustic waves
Single-electron transport driven by surface acoustic waves (SAW) through a
narrow constriction, formed in two-dimensional electron gas, is studied
theoretically. Due to long-range Coulomb interaction, the tunneling coupling
between the electron gas and the moving minimum of the SAW-induced potential
rapidly decays with time. As a result, nonadiabaticiy sets a limit for the
accuracy of the quantization of acoustoelectric current
Quantized Adiabatic Charge Transport in a Carbon Nanotube
The coupling of a metallic Carbon nanotube to a surface acoustic wave (SAW)
is proposed as a vehicle to realize quantized adiabatic charge transport in a
Luttinger liquid system. We demonstrate that electron backscattering by a
periodic SAW potential, which results in miniband formation, can be achieved at
energies near the Fermi level. Electron interaction, treated in a Luttinger
liquid framework, is shown to enhance minigaps and thereby improve current
quantization. Quantized SAW induced current, as a function of electron density,
changes sign at half-filling.Comment: 5 pages, 2 figure
Charge pumping in carbon nanotube quantum dots
We investigate charge pumping in carbon nanotube quantum dots driven by the
electric field of a surface acoustic wave. We find that at small driving
amplitudes, the pumped current reverses polarity as the conductance is tuned
through a Coulomb blockade peak using a gate electrode. We study the behavior
as a function of wave amplitude, frequency and direction and develop a model in
which our results can be understood as resulting from adiabatic charge
redistribution between the leads and quantum dots on the nanotube
Single-qubit gates and measurements in the surface acoustic wave quantum computer
In the surface acoustic wave quantum computer, the spin state of an electron
trapped in a moving quantum dot comprises the physical qubit of the scheme. Via
detailed analytic and numerical modeling of the qubit dynamics, we discuss the
effect of excitations into higher-energy orbital states of the quantum dot that
occur when the qubits pass through magnetic fields. We describe how
single-qubit quantum operations, such as single-qubit rotations and
single-qubit measurements, can be performed using only localized static
magnetic fields. The models provide useful parameter regimes to be explored
experimentally when the requirements on semiconductor gate fabrication and the
nanomagnetics technology are met in the future.Comment: 13 pages, 10 figures, submitted to Phys. Rev.
High Frequency Acousto-electric Single Photon Source
We propose a single optical photon source for quantum cryptography based on the acousto-electric effect. Surface acoustic waves (SAWs) propagating through a quasi-one-dimensional channel have been shown to produce packets of electrons which reside in the SAW minima and travel at the velocity of sound. In our scheme these electron packets are injected into a p-type region, resulting in photon emission. Since the number of electrons in each packet can be controlled down to a single electron, a stream of single (or N) photon states, with a creation time strongly correlated with the driving acoustic field, should be generated