65 research outputs found
Coherent Electron-Phonon Coupling in Tailored Quantum Systems
The coupling between a two-level system and its environment leads to
decoherence. Within the context of coherent manipulation of electronic or
quasiparticle states in nanostructures, it is crucial to understand the sources
of decoherence. Here, we study the effect of electron-phonon coupling in a
graphene and an InAs nanowire double quantum dot. Our measurements reveal
oscillations of the double quantum dot current periodic in energy detuning
between the two levels. These periodic peaks are more pronounced in the
nanowire than in graphene, and disappear when the temperature is increased. We
attribute the oscillations to an interference effect between two alternative
inelastic decay paths involving acoustic phonons present in these materials.
This interpretation predicts the oscillations to wash out when temperature is
increased, as observed experimentally.Comment: 11 pages, 4 figure
A quantum spin transducer based on nano electro-mechancial resonator arrays
Implementation of quantum information processing faces the contradicting
requirements of combining excellent isolation to avoid decoherence with the
ability to control coherent interactions in a many-body quantum system. For
example, spin degrees of freedom of electrons and nuclei provide a good quantum
memory due to their weak magnetic interactions with the environment. However,
for the same reason it is difficult to achieve controlled entanglement of spins
over distances larger than tens of nanometers. Here we propose a universal
realization of a quantum data bus for electronic spin qubits where spins are
coupled to the motion of magnetized mechanical resonators via magnetic field
gradients. Provided that the mechanical system is charged, the magnetic moments
associated with spin qubits can be effectively amplified to enable a coherent
spin-spin coupling over long distances via Coulomb forces. Our approach is
applicable to a wide class of electronic spin qubits which can be localized
near the magnetized tips and can be used for the implementation of hybrid
quantum computing architectures
Radio frequency measurements of tunnel couplings and singlet–triplet spin states in Si:P quantum dots
Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet–triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot–lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon
Spin Relaxation in Ge/Si Core-Shell Nanowire Qubits
Controlling decoherence is the most challenging task in realizing quantum
information hardware. Single electron spins in gallium arsenide are a leading
candidate among solid- state implementations, however strong coupling to
nuclear spins in the substrate hinders this approach. To realize spin qubits in
a nuclear-spin-free system, intensive studies based on group-IV semiconductor
are being pursued. In this case, the challenge is primarily control of
materials and interfaces, and device nanofabrication. We report important steps
toward implementing spin qubits in a predominantly nuclear-spin-free system by
demonstrating state preparation, pulsed gate control, and charge-sensing spin
readout of confined hole spins in a one-dimensional Ge/Si nanowire. With fast
gating, we measure T1 spin relaxation times in coupled quantum dots approaching
1 ms, increasing with lower magnetic field, consistent with a spin-orbit
mechanism that is usually masked by hyperfine contributions
One dimensional transport in silicon nanowire junction-less field effect transistors
Junction-less nanowire transistors are being investigated to solve short channel effects
in future CMOS technology. Here we demonstrate 8 nm diameter silicon
nanowire junction-less transistors with metallic doping densities which demonstrate
clear 1D electronic transport characteristics. The 1D regime allows excellent gate
modulation with near ideal subthreshold slopes, on- to off-current ratios above 108
and high on-currents at room temperature. Universal conductance scaling as a function
of voltage and temperature similar to previous reports of Luttinger liquids and
Coulomb gap behaviour at low temperatures suggests that many body effects including
electron-electron interactions are important in describing the electronic transport.
This suggests that modelling of such nanowire devices will require 1D models which
include many body interactions to accurately simulate the electronic transport to
optimise the technology but also suggest that 1D effects could be used to enhance
future transistor performance
Spin and orbital structure of the first six holes in a silicon metal-oxide-semiconductor quantum dot
- …