ELFT HÍRADÓ

[andraspalyi AT caesar.elte.hu]

Az ELTE Nanofizika Szeminarium jovo hetfoi eloadasa:

Edward Laird (TU Delft, Hollandia): Gigahertz nanomechanics and a
valley-spin qubit in carbon nanotubes

Helyszin: ELTE Eszaki Tomb, 5.55-os terem (1117 Budapest, Pazmany
Peter setany 1/A),
Idopont: 2012. november 05. hetfo, 10:15

Kivonat:
"Carbon nanotubes are versatile materials in which many aspects of
condensed matter physics come together. Recent progress in fabrication
has allowed the creation of low-disorder devices in which delicate
effects can be studied in electrical transport. I will present two
experiments measuring the motion of a suspended nanotube, and
demonstrating a nanotube valley-spin qubit.
In the first part, I will describe a high-quality, high frequency
mchanical resonator. Nanotubes combine light mass (leading to large
zero-point motion) and high stiffness (leading to large mode spacing),
making them potentially interesting for studying the quantum limit of
mechanical motion. We have created a nanotube resonator with a series
of modes extending to 39 GHz with a quality factor of 33 000 in the
highest mode. This unprecedentedly high combination corresponds to a
thermal excited state probability below 10^{-8} and a relaxation
time of 140 ns (with microsecond relaxation times for lower modes).
The effect of electron tunneling on the mechanical resonance is found
to depend on frequency as the tunneling time becomes comparable to the
vibration period.
In the second part, I will present a qubit in a nanotube. Nanotubes
are attractive materials for electron spin qubits because they can be
made free of hyperfine dephasing and because spin-orbit interaction
offers a route to all-electrical spin control. However, the existence
of the valley degree of freedom and unscreened Coulomb interaction
make the qubit readout complicated. Using a new fabrication technique,
we have demonstrated combined valley-spin Pauli blockade in a nanotube
double quantum dot by exploiting the bandgap to increase the energy
splitting between blocked and unblocked states. This effect provides a
readout mechanism for a qubit based on two valley-spin states of an
electron. Making use of spin-orbit coupling in a bent nanotube, we
drive coherent rotations between the qubit states, and demonstrate
universal qubit control. The coherence time is found to be 65 ns,
surprisingly short given the low density of nuclear spins. I will
discuss prospects for coupling this qubit to the mechanical motion of
the nanotube and thereby achieving complete quantum control over the
motional state of the device."

Minden erdeklodot szivesen latunk.

A szeminarium tovabbi programja:
http://wigner.elte.hu/koltai/science/?q=seminar

Udvozlettel,
Palyi Andras