17 research outputs found
Error-resistant Single Qubit Gates with Trapped Ions
Coherent operations constitutive for the implementation of single and
multi-qubit quantum gates with trapped ions are demonstrated that are robust
against variations in experimental parameters and intrinsically indeterministic
system parameters. In particular, pulses developed using optimal control theory
are demonstrated for the first time with trapped ions. Their performance as a
function of error parameters is systematically investigated and compared to
composite pulses.Comment: 5 pages 5 figure
A relaxationless demonstration of the Quantum Zeno Paradox on an individual atom
The driven evolution of the spin of an individual atomic ion on the
ground-state hyperfine resonance is impeded by the observation of the ion in
one of the pertaining eigenstates. Detection of resonantly scattered light
identifies the ion in its upper ``bright'' state. The lower ``dark'' ion state
is free of relaxation and correlated with the detector by a null signal. Null
events represent the straightforward demonstration of the quantum Zeno paradox.
Also, high probability of survival was demonstrated when the ion, driven by a
fractionated pulse, was probed {\em and monitored} during the
intermissions of the drive, such that the ion's evolution is completely
documented.Comment: 7 page
Simultaneous cooling of axial vibrational modes in a linear ion-trap
In order to use a collection of trapped ions for experiments where a well defined preparation of vibrational states is necessary (for example, for quantum information processing), all vibrational modes have to be cooled to ensure precise and repeatable manipulation of quantum states of internal and external degrees of freedom of the ions. A method for simultaneous sideband cooling of all axial vibrational modes is proposed. By application of a magnetic field gradient the absorption spectrum of each ion is modified such that sideband resonances of different vibrational modes coincide. The ion string is then irradiated with electromagnetic radiation of only a single frequency in the optical or microwave regime for sideband excitation. This new cooling scheme is described with an analytical treatment and investigated in detailed numerical studies
Individual addressing of trapped ions and coupling of motional and spin states using rf radiation
Individual electrodynamically trapped and laser cooled ions are addressed in
frequency space using radio-frequency radiation in the presence of a static
magnetic field gradient. In addition, an interaction between motional and spin
states induced by an rf field is demonstrated employing rf-optical double
resonance spectroscopy. These are two essential experimental steps towards
realizing a novel concept for implementing quantum simulations and quantum
computing with trapped ions.Comment: Replaced with published versio
High-fidelity quantum driving
The ability to accurately control a quantum system is a fundamental
requirement in many areas of modern science such as quantum information
processing and the coherent manipulation of molecular systems. It is usually
necessary to realize these quantum manipulations in the shortest possible time
in order to minimize decoherence, and with a large stability against
fluctuations of the control parameters. While optimizing a protocol for speed
leads to a natural lower bound in the form of the quantum speed limit rooted in
the Heisenberg uncertainty principle, stability against parameter variations
typically requires adiabatic following of the system. The ultimate goal in
quantum control is to prepare a desired state with 100% fidelity. Here we
experimentally implement optimal control schemes that achieve nearly perfect
fidelity for a two-level quantum system realized with Bose-Einstein condensates
in optical lattices. By suitably tailoring the time-dependence of the system's
parameters, we transform an initial quantum state into a desired final state
through a short-cut protocol reaching the maximum speed compatible with the
laws of quantum mechanics. In the opposite limit we implement the recently
proposed transitionless superadiabatic protocols, in which the system perfectly
follows the instantaneous adiabatic ground state. We demonstrate that
superadiabatic protocols are extremely robust against parameter variations,
making them useful for practical applications.Comment: 17 pages, 4 figure