204 research outputs found
Real-time detection of single electron tunneling using a quantum point contact
We observe individual tunnel events of a single electron between a quantum
dot and a reservoir, using a nearby quantum point contact (QPC) as a charge
meter. The QPC is capacitively coupled to the dot, and the QPC conductance
changes by about 1% if the number of electrons on the dot changes by one. The
QPC is voltage biased and the current is monitored with an IV-convertor at room
temperature. We can resolve tunnel events separated by only 8 s, limited
by noise from the IV-convertor. Shot noise in the QPC sets a 25 ns lower bound
on the accessible timescales.Comment: 3 pages, 3 figures, submitte
ΠΡΡΡΡΠΎΠ΄Π΅ΠΉΡΡΠ²ΡΡΡΠ°Ρ ΡΠΈΡΡΠ΅ΠΌΠ° ΡΡΠ°Π±ΠΈΠ»ΠΈΠ·Π°ΡΠΈΠΈ ΠΏΠ΅ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠ³ΠΎ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ
Π Π°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°Π΅ΡΡΡ ΡΠΈΡΡΠ΅ΠΌΠ° ΡΡΠ°Π±ΠΈΠ»ΠΈΠ·Π°ΡΠΈΠΈ ΠΏΠ΅ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠ³ΠΎ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎ-ΠΏΠΎΠ»ΡΠΏΡΠΎΠ²ΠΎΠ΄Π½ΠΈΠΊΠΎΠ²ΠΎΠ³ΠΎ ΡΠ΅Π³ΡΠ»ΡΡΠΎΡΠ° Π±Π΅Π· ΠΏΠΎΠ΄ΠΌΠ°Π³Π½ΠΈΡΠΈΠ²Π°Π½ΠΈΡ ΠΏΠΎΡΡΠΎΡΠ½Π½ΡΠΌ ΡΠΎΠΊΠΎΠΌ ΠΈ Π±ΡΡΡΡΠΎΠ΄Π΅ΠΉΡΡΠ²ΡΡΡΠ΅ΠΉ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΠΈ. ΠΠΎ ΠΎΠΏΠΈΡΠ°Π½Π½ΠΎΠΌΡ ΠΏΡΠΈΠ½ΡΠΈΠΏΡ ΠΌΠΎΠ³ΡΡ Π±ΡΡΡ ΠΏΠΎΡΡΡΠΎΠ΅Π½Ρ Π±ΡΡΡΡΠΎΠ΄Π΅ΠΉΡΡΠ²ΡΡΡΠΈΠ΅ ΠΎΠ΄Π½ΠΎΡΠ°Π·Π½ΡΠ΅ ΠΈ ΡΡΠ΅Ρ
ΡΠ°Π·Π½ΡΠ΅ ΡΡΠ°Π±ΠΈΠ»ΠΈΠ·Π°ΡΠΎΡΡ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ Π½Π° Π²ΡΡΡΠ΅ΡΠ½ΠΎ-ΠΏΠ°ΡΠ°Π»Π»Π΅Π»ΡΠ½ΡΡ
ΡΠΏΡΠ°Π²Π»ΡΠ΅ΠΌΡΡ
Π²Π΅Π½ΡΠΈΠ»ΡΡ
ΠΏΡΠΈ ΠΈΡ
Π΅ΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΈΠ»ΠΈ ΠΏΡΠΈΠ½ΡΠ΄ΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΠΊΠΎΠΌΠΌΡΡΠ°ΡΠΈΠΈ
Cotunneling-mediated transport through excited states in the Coulomb blockade regime
We present finite bias transport measurements on a few-electron quantum dot.
In the Coulomb blockade regime, strong signatures of inelastic cotunneling
occur which can directly be assigned to excited states observed in the
non-blockaded regime. In addition, we observe structures related to sequential
tunneling through the dot, occuring after it has been excited by an inelastic
cotunneling process. We explain our findings using transport calculations
within the real-time Green's function approach, including diagrams up to fourth
order in the tunneling matrix elements.Comment: 4 pages, 3 figure
Peak Effect in Superconductors: Absence of Phase Transition and Possibility of Jamming in Vortex Matter
The magnetic field dependence of the critical current for the
vortex phase of a disordered superconductor is studied numerically at zero
temperature. The increases rapidly near the upper critical field
similar to the peak effect (PE) phenomenon observed in many
superconductors. The real space configuration across the PE changes
continuously from a partially ordered domain (polycrystalline) state into an
amorphous state. The topological defect density
with for . There is no evidence of a phase transition in
the vicinity of the PE suggesting that an order-disorder transition is not
essential for the occurrence of the PE phenomenon. An alternative view is
presented wherein the vortex system with high dislocation density undergoes
jamming at the onset of the PE.Comment: 8 pages and 5 figure
Real Time Electron Tunneling and Pulse Spectroscopy in Carbon Nanotube Quantum Dots
We investigate a Quantum Dot (QD) in a Carbon Nanotube (CNT) in the regime
where the QD is nearly isolated from the leads. An aluminum single electron
transistor (SET) serves as a charge detector for the QD. We precisely measure
and tune the tunnel rates into the QD in the range between 1 kHz and 1 Hz,
using both pulse spectroscopy and real - time charge detection and measure the
excitation spectrum of the isolated QD.Comment: 12 pages, 5 figure
Immersive media practices in the classroom: models of the teaching research nexus in an Australian context
Electrical manipulation of spin states in a single electrostatically gated transition-metal complex
We demonstrate an electrically controlled high-spin (S=5/2) to low-spin
(S=1/2) transition in a three-terminal device incorporating a single Mn2+ ion
coordinated by two terpyridine ligands. By adjusting the gate-voltage we reduce
the terpyridine moiety and thereby strengthen the ligand-field on the Mn-atom.
Adding a single electron thus stabilizes the low-spin configuration and the
corresponding sequential tunnelling current is suppressed by spin-blockade.
From low-temperature inelastic cotunneling spectroscopy, we infer the
magnetic excitation spectrum of the molecule and uncover also a strongly
gate-dependent singlet-triplet splitting on the low-spin side. The measured
bias-spectroscopy is shown to be consistent with an exact diagonalization of
the Mn-complex, and an interpretation of the data is given in terms of a
simplified effective model.Comment: Will appear soon in Nanoletter
ΠΠ»Π°Π·ΠΌΠ΅Π½Π½Π°Ρ ΠΏΠ΅ΡΠ΅ΡΠ°Π±ΠΎΡΠΊΠ° ΠΏΠΎΡΠΎΡΠΊΠΎΠ² ΠΎΠΊΡΠΈΠ΄ΠΎΠ² ΠΌΠ΅ΡΠ°Π»Π»ΠΎΠ²
ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½Ρ Π½Π° ΠΈΠ·ΡΡΠ΅Π½ΠΈΠ΅ ΠΌΠΈΠΊΡΠΎΡΡΡΡΠΊΡΡΡΡ ΠΏΠΎΡΠΎΡΠΊΠ°, ΠΏΡΠΎΡΠ΅Π΄ΡΠ΅Π³ΠΎ ΠΏΠ»Π°Π·ΠΌΠ΅Π½Π½ΡΡ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΡ. ΠΡΠΎΠ±ΠΎΠ΅ Π²Π½ΠΈΠΌΠ°Π½ΠΈΠ΅ Π±ΡΠ΄Π΅Ρ ΡΠ΄Π΅Π»Π΅Π½ΠΎ ΡΠΎΡ
ΡΠ°Π½Π½ΠΎΡΡΠΈ ΠΏΠΎΡΠΎΡΠΊΠ° ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²Π° ΠΏΠΎΡΠΎΡΠΊΠ°The research is aimed at studying the microstructure of the powder that has undergone plasma treatment. Particular attention will be paid to the preservation of the amount of powder
Conditional statistics of electron transport in interacting nanoscale conductors
Interactions between nanoscale semiconductor structures form the basis for
charge detectors in the solid state. Recent experimental advances have
demonstrated the on-chip detection of single electron transport through a
quantum dot (QD). The discreteness of charge in units of e leads to intrinsic
fluctuations in the electrical current, known as shot noise. To measure these
single-electron fluctuations a nearby coherent conductor, called a quantum
point contact (QPC), interacts with the QD and acts as a detector. An important
property of the QPC charge detector is noninvasiveness: the system physically
affects the detector, not visa-versa. Here we predict that even for ideal
noninvasive detectors such as the QPC, when a particular detector result is
observed, the system suffers an informational backaction, radically altering
the statistics of transport through the QD as compared to the unconditional
shot noise. We develop a theoretical model to make predictions about the joint
current probability distributions and conditional transport statistics. The
experimental findings reported here demonstrate the reality of informational
backaction in nanoscale systems as well as a variety of new effects, such as
conditional noise enhancement, which are in essentially perfect agreement with
our model calculations. This type of switching telegraph process occurs
abundantly in nature, indicating that these results are applicable to a wide
variety of systems.Comment: 16 pages, 3 figures, to appear in Nature Physic
Driven coherent oscillations of a single electron spin in a quantum dot
The ability to control the quantum state of a single electron spin in a
quantum dot is at the heart of recent developments towards a scalable
spin-based quantum computer. In combination with the recently demonstrated
exchange gate between two neighbouring spins, driven coherent single spin
rotations would permit universal quantum operations. Here, we report the
experimental realization of single electron spin rotations in a double quantum
dot. First, we apply a continuous-wave oscillating magnetic field, generated
on-chip, and observe electron spin resonance in spin-dependent transport
measurements through the two dots. Next, we coherently control the quantum
state of the electron spin by applying short bursts of the oscillating magnetic
field and observe about eight oscillations of the spin state (so-called Rabi
oscillations) during a microsecond burst. These results demonstrate the
feasibility of operating single-electron spins in a quantum dot as quantum
bits.Comment: Total 25 pages. 11 pages main text, 5 figures, 9 pages supplementary
materia
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