20,898 research outputs found
Measurement Back-Action in Quantum Point-Contact Charge Sensing
Charge sensing with quantum point-contacts (QPCs) is a technique widely used in semiconductor quantum-dot research. Understanding the physics of this measurement process, as well as finding ways of suppressing unwanted measurement back-action, are therefore both desirable. In this article, we present experimental studies targeting these two goals. Firstly, we measure the effect of a QPC on electron tunneling between two InAs quantum dots, and show that a model based on the QPC’s shot-noise can account for it. Secondly, we discuss the possibility of lowering the measurement current (and thus the back-action) used for charge sensing by correlating the signals of two independent measurement channels. The performance of this method is tested in a typical experimental setup.Swiss National Science Foundatio
Fast Single-Charge Sensing with an rf Quantum Point Contact
We report high-bandwidth charge sensing measurements using a GaAs quantum
point contact embedded in a radio frequency impedance matching circuit
(rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to
charge, we demonstrate a conductance sensitivity of 5x10^(-6) e^(2)/h Hz^(-1/2)
with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron
double quantum dot is investigated in a mode where the rf-QPC back-action is
rapidly switched.Comment: related papers available at http://marcuslab.harvard.ed
Latched Detection of Excited States in an Isolated Double Quantum Dot
Pulsed electrostatic gating combined with capacitive charge sensing is used
to perform excited state spectroscopy of an electrically isolated
double-quantum-dot system. The tunneling rate of a single charge moving between
the two dots is affected by the alignment of quantized energy levels; measured
tunneling probabilities thereby reveal spectral features. Two pulse sequences
are investigated, one of which, termed latched detection, allows measurement of
a single tunneling event without repetition. Both provide excited-state
spectroscopy without electrical contact to the double-dot system.Comment: related papers available at http://marcuslab.harvard.ed
Charge sensing in carbon nanotube quantum dots on microsecond timescales
We report fast, simultaneous charge sensing and transport measurements of
gate-defined carbon nanotube quantum dots. Aluminum radio frequency single
electron transistors (rf-SETs) capacitively coupled to the nanotube dot provide
single-electron charge sensing on microsecond timescales. Simultaneously, rf
reflectometry allows fast measurement of transport through the nanotube dot.
Charge stability diagrams for the nanotube dot in the Coulomb blockade regime
show extended Coulomb diamonds into the high-bias regime, as well as even-odd
filling effects, revealed in charge sensing data.Comment: 4 pages, 4 figure
Back action of graphene charge detectors on graphene and carbon nanotube quantum dots
We report on devices based on graphene charge detectors (CDs) capacitively
coupled to graphene and carbon nanotube quantum dots (QDs). We focus on back
action effects of the CD on the probed QD. A strong influence of the bias
voltage applied to the CD on the current through the QD is observed. Depending
on the charge state of the QD the current through the QD can either strongly
increase or completely reverse as a response to the applied voltage on the CD.
To describe the observed behavior we employ two simple models based on single
electron transport in QDs with asymmetrically broadened energy distributions of
the source and the drain leads. The models successfully explain the back action
effects. The extracted distribution broadening shows a linear dependency on the
bias voltage applied to the CD. We discuss possible mechanisms mediating the
energy transfer between the CD and QD and give an explanation for the origin of
the observed asymmetry.Comment: 6 pages, 4 figure
Spins in few-electron quantum dots
This review describes the physics of spins in quantum dots containing one or
two electrons, from an experimentalist's viewpoint. Various methods for
extracting spin properties from experiment are presented, restricted
exclusively to electrical measurements. Furthermore, experimental techniques
are discussed that allow for: (1) the rotation of an electron spin into a
superposition of up and down, (2) the measurement of the quantum state of an
individual spin and (3) the control of the interaction between two neighbouring
spins by the Heisenberg exchange interaction. Finally, the physics of the
relevant relaxation and dephasing mechanisms is reviewed and experimental
results are compared with theories for spin-orbit and hyperfine interactions.
All these subjects are directly relevant for the fields of quantum information
processing and spintronics with single spins (i.e. single-spintronics).Comment: final version (52 pages, 49 figures), Rev. Mod. Phy
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