130 research outputs found
Zeno and anti-Zeno polarization control of spin-ensembles by induced dephasing
We experimentally and theoretically demonstrate the purity (polarization)
control of qubits entangled with multiple spins, using induced dephasing in
nuclear magnetic resonance (NMR) setups to simulate repeated quantum
measurements. We show that one may steer the qubit ensemble towards a
quasi-equilibrium state of certain purity, by choosing suitable time intervals
between dephasing operations. These results demonstrate that repeated dephasing
at intervals associated with the anti-Zeno regime lead to ensemble
purification, whereas those associated with the Zeno regime lead to ensemble
mixing.Comment: Main Text: 5 pages, 2 figures. Sup. Inf.: 5pages, 1 figur
Perfect state transfers by selective quantum interferences within complex spin networks
We present a method that implement directional, perfect state transfers
within a branched spin network by exploiting quantum interferences in the
time-domain. That provides a tool to isolate subsystems from a large and
complex one. Directionality is achieved by interrupting the spin-spin coupled
evolution with periods of free Zeeman evolutions, whose timing is tuned to be
commensurate with the relative phases accrued by specific spin pairs. This
leads to a resonant transfer between the chosen qubits, and to a detuning of
all remaining pathways in the network, using only global manipulations. As the
transfer is perfect when the selected pathway is mediated by 2 or 3 spins,
distant state transfers over complex networks can be achieved by successive
recouplings among specific pairs/triads of spins. These effects are illustrated
with a quantum simulator involving 13C NMR on Leucine's backbone; a six-spin
network.Comment: 5 pages, 3 figure
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