61 research outputs found
Distinguishability of hyperentangled Bell state by linear evolution and local projective measurement
Measuring an entangled state of two particles is crucial to many quantum
communication protocols. Yet Bell state distinguishability using a finite
apparatus obeying linear evolution and local measurement is theoretically
limited. We extend known bounds for Bell-state distinguishability in one and
two variables to the general case of entanglement in two-state variables.
We show that at most classes out of hyper-Bell states can be
distinguished with one copy of the input state. With two copies, complete
distinguishability is possible. We present optimal schemes in each case.Comment: 5 pages, 2 figure
ISOTOPE SHIFT SPECTROSCOPY OF ULTRACOLD STRONTIUM
We describe the design, construction, and performance of a laser system to probe the ultra-narrow (Ξ/2Ο β mHz) clock transition 1S0 β 3P0 in strontium. We present the first reported spectroscopy of this transition in two of the bosonic isotopes, 84Sr and 86Sr. Furthermore, we measure the complete set of isotope shifts between all four stable isotopes on the clock line and the narrow intercombination line 1S0 β 3P1, permitting a King plot analysis of the isotope shifts. Complications arising from the unambiguous determination of a line center in 87Sr 3P1 prevent us from making claims about the King linearity, but we provide a statistical boot- strap analysis of the isotope shifts 88β84Sr and 88β86Sr to compute a field shift ratio F698/F689 = 0.9979, with a 95% confidence interval [0.9952,1.0008]. The intercept term K698 β (F698/F689) K689 is similarly determined to be -2.0 GHz-amu, with a 95% confidence interval [β3.9, β0.3] GHz-amu. Finally, we describe the design of a next-generation apparatus that will enable improvements on the results described
here, as well as other studies that involve coherent manipulation of strontium atoms on the clock line
Extremum seeking control of quantum gates
To be useful for quantum computation, gate operations must be maintained at
high fidelities over long periods of time. In addition to decoherence, slow
drifts in control hardware leads to inaccurate gates, causing the quality of
operation of as-built quantum computers to vary over time. Here, we demonstrate
a data-driven approach to stabilized control, combining extremum-seeking
control (ESC) with direct randomized benchmarking (DRB) to stabilize two-qubit
gates under unknown control parameter fluctuations. As a case study, we
consider these control strategies in the context of a trapped ion quantum
computer using physically-realistic simulation. We then experimentally
demonstrate this control strategy on a state-of-the-art, commercial trapped-ion
quantum computer.Comment: 5 pages, 6 figure
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