865 research outputs found
Spin state readout by quantum jump technique: for the purpose of quantum computing
Utilizing the Pauli-blocking mechanism we show that shining circular
polarized light on a singly-charged quantum dot induces spin dependent
fluorescence. Employing the quantum-jump technique we demonstrate that this
resonance luminescence, due to a spin dependent optical excitation, serves as
an excellent readout mechanism for measuring the spin state of a single
electron confined to a quantum dot.Comment: 11 pages, 4 eps figure
Spin-based optical quantum gates via Pauli blocking in semiconductor quantum dots
We present a solid-state implementation of ultrafast conditional quantum
gates. Our proposal for a quantum-computing device is based on the spin degrees
of freedom of electrons confined in semiconductor quantum dots, thus benefiting
from relatively long decoherence times. More specifically, combining Pauli
blocking effects with properly tailored ultrafast laser pulses, we are able to
obtain sub-picosecond spin-dependent switching of the Coulomb interaction,
which is the essence of our conditional phase-gate proposal. This allows us to
realize {\it a fast two qubit gate which does not translate into fast
decoherence times} and paves the road for an all-optical spin-based quantum
computer.Comment: 14 Pages RevTeX, 3 eps figures include
A simple quantum gate with atom chips
We present a simple scheme for implementing an atomic phase gate using two
degrees of freedom for each atom and discuss its realization with cold rubidium
atoms on atom chips. We investigate the performance of this collisional phase
gate and show that gate operations with high fidelity can be realized in
magnetic traps that are currently available on atom chips.Comment: 7 pages, 7 figures. One missing reference added in v2. To appear in
European Physical Journal
The Quantum Speed Limit of Optimal Controlled Phasegates for Trapped Neutral Atoms
We study controlled phasegates for ultracold atoms in an optical potential. A
shaped laser pulse drives transitions between the ground and electronically
excited states where the atoms are subject to a long-range 1/R^3 interaction.
We fully account for this interaction and use optimal control theory to
calculate the pulse shapes. This allows us to determine the minimum pulse
duration, respectively, gate time T that is required to obtain high fidelity.
We accurately analyze the speed limiting factors, and we find the gate time to
be limited either by the interaction strength in the excited state or by the
ground state vibrational motion in the trap. The latter needs to be resolved by
the pulses in order to fully restore the motional state of the atoms at the end
of the gate.Comment: 11 pages, 10 figures, 1 tabl
Impulsive quantum measurements: restricted path integral versus von Neumann collapse
The relation between the restricted path integral approach to quantum
measurement theory and the commonly accepted von Neumann wavefunction collapse
postulate is presented. It is argued that in the limit of impulsive
measurements the two approaches lead to the same predictions. The example of
repeated impulsive quantum measurements of position performed on a harmonic
oscillator is discussed in detail and the quantum nondemolition strategies are
recovered in both the approaches.Comment: 12 pages, 3 figure
- …