Qubits measured in a different light

Anonymous

Anne E. B. Nielsen

A parity measurement on two qubits, each consisting of a single atom in a cavity, can be realized by measuring the phase shift of a probe beam which interacts sequentially with the two qubits, but imperfections lead to decoherence within the subspaces of a given parity. We demonstrate that a different setup, where the probe light interacts repeatedly with the qubits, can reduce the rate of decoherence within the odd- or the even-parity subspace significantly. We consider both the case of a resonant and the case of a nonresonant light-atom interaction and find that the performance is comparable if the parameters are chosen appropriately.

Daniel Cavalcanti, Pablo L. Saldanha, Olavo Cosme +5 more

We develop a general approach to investigate the geometry of the set of different kinds of entangled states. We provide the first measurements of the border of the set of separable states for two qubits.

John Gaebler, Charles H. Baldwin, Steven A. Moses +5 more

Midcircuit measurement and reset are crucial primitives in quantum computation, but such operations require strong interactions with selected qubits while maintaining isolation of neighboring qubits, which is a significant challenge in many systems. For trapped ion systems, measurement is performed with laser-induced fluorescence. Stray light from the detection beam and fluorescence from the measured ions can be significant sources of decoherence for unmeasured qubits. We present a technique using ion micromotion to reduce these sources of decoherence by over an order of magnitude. We benchmark the performance with a different method, based on randomized benchmarking, to estimate the magnitude of crosstalk errors on nearby qubits. Using the Honeywell System Model H0, we demonstrate measurement and reset on select qubits with low crosstalk errors on neighboring qubits.

Anonymous