519 research outputs found
Full control of quadruple quantum dot circuit charge states in the single electron regime
We report the realization of an array of four tunnel coupled quantum dots in
the single electron regime, which is the first required step toward a scalable
solid state spin qubit architecture. We achieve an efficient tunability of the
system but also find out that the conditions to realize spin blockade readout
are not as straightforwardly obtained as for double and triple quantum dot
circuits. We use a simple capacitive model of the series quadruple quantum dots
circuit to investigate its complex charge state diagrams and are able to find
the most suitable configurations for future Pauli spin blockade measurements.
We then experimentally realize the corresponding charge states with a good
agreement to our model.Comment: 4 pages, 3 figure
Photon mediated interaction between distant quantum dot circuits
Engineering the interaction between light and matter is an important goal in
the emerging field of quantum opto-electronics. Thanks to the use of cavity
quantum electrodynamics architectures, one can envision a fully hybrid
multiplexing of quantum conductors. Here, we use such an architecture to couple
two quantum dot circuits . Our quantum dots are separated by 200 times their
own size, with no direct tunnel and electrostatic couplings between them. We
demonstrate their interaction, mediated by the cavity photons. This could be
used to scale up quantum bit architectures based on quantum dot circuits or
simulate on-chip phonon-mediated interactions between strongly correlated
electrons
Harnessing spin precession with dissipation
International audienceNon-collinear spin transport is at the heart of spin or magnetization control in spintronics devices. The use of nanoscale conductors exhibiting quantum effects in transport could provide new paths for that purpose. Here we study non-collinear spin transport in a quantum dot. We use a device made out of a single-wall carbon nanotube connected to orthogonal ferromagnetic electrodes. In the spin transport signals, we observe signatures of out of equilibrium spin precession that are electrically tunable through dissipation. This could provide a new path to harness spin precession in nanoscale conductors
A fast quantum interface between different spin qubit encodings
Single-spin qubits in semiconductor quantum dots proposed by Loss and
DiVincenzo (LD qubits) hold promise for universal quantum computation with
demonstrations of a high single-qubit gate fidelity above 99.9 % and two-qubit
gates in conjunction with a long coherence time. However, initialization and
readout of a qubit is orders of magnitude slower than control, which is
detrimental for implementing measurement-based protocols such as
error-correcting codes. In contrast, a singlet-triplet (ST) qubit, encoded in a
two-spin subspace, has the virtue of fast readout with high fidelity and
tunable coupling to the electric field. Here, we present a hybrid system which
benefits from the different advantages of these two distinct spin-qubit
implementations. A quantum interface between the two codes is realized by
electrically tunable inter-qubit exchange coupling. We demonstrate a
controlled-phase (CPHASE) gate that acts within 5.5 ns, much faster than the
measured dephasing time of 211 ns. The presented hybrid architecture will be
useful to settle remaining key problems with building scalable spin-based
quantum computers
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