17 research outputs found
High-fidelity quantum control by polychromatic pulse trains
We introduce a quantum control technique using polychromatic pulse sequences
(PPS), consisting of pulses with different carrier frequencies, i.e. different
detunings with respect to the qubit transition frequency. We derive numerous
PPS, which generate broadband, narrowband, and passband excitation profiles for
different target transition probabilities. This makes it possible to create
high-fidelity excitation profiles which are either (i) robust to deviations in
the experimental parameters, which is attractive for quantum computing, or (ii)
more sensitive to such variations, which is attractive for cross talk
elimination and quantum sensing. The method is demonstrated experimentally
using one of IBM's superconducting quantum processors, in a very good agreement
between theory and experiment. These results demonstrate both the excellent
coherence properties of the IBM qubits and the accuracy, robustness and
flexibility of the proposed quantum control technique. They also show that the
detuning is as efficient control parameter as the pulse phase that is commonly
used in composite pulses. Hence the method opens a variety of perspectives for
quantum control in areas where phase manipulation is difficult or inaccurate.Comment: 5 pages, 4 figure
Variable Ultra-broadband and Narrowband Composite Polarization Retarders
We propose and experimentally demonstrate novel types of composite sequences
of half-wave and quarter-wave polarization retarders, either permitting
operation at ultra-broad spectral bandwidth or narrow bandwidth. The retarders
are composed of stacked standard half-wave retarders and quarter-wave retarders
of equal thickness. To our knowledge, these home-built devices outperform all
commercially available compound retarders, made of several birefringent
materials.Comment: 5 figures, 9 page
Simulation of Jahn-Teller-Dicke Magnetic Structural Phase Transition with Trapped Ions
We study theoretically the collective Ee Jahn-Teller-Dicke
distortion in a system of trapped ions. We focus in the limit of infinite range
interactions in which an ensemble of effective spins interacts with two
collective vibrational modes with U(1) symmetric couplings. Our model is
exactly solvable in the thermodynamical limit and it is amenable to be solved
by exact numerical diagonalization for a moderate number of ions. We show that
trapped ions are ideally suited to study the emergence of spontaneous symmetry
breaking of a continuous symmetry and magnetic structural phase transition in a
mesoscopic system.Comment: 19 pages, 7 figure
Highly efficient broadband conversion of light polarization by composite retarders
Driving on an analogy with the technique of composite pulses in quantum
physics, we propose highly efficient broadband polarization converters composed
of sequences of ordinary retarders rotated at specific angles with respect to
their fast-polarization axes.Comment: 5 pages, 3 figures; check JOSA A 201