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arXiv:1210.6407 · Physical Review Letters

Individual-Ion Addressing with Microwave Field Gradients

Ulrich Warring, C. Ospelkaus, Yves Colombe, Robert Jördens, Dietrich G. Leibfried, David J. Wineland

Published Apr 22, 2013• 66 citations
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Abstract

Individual-qubit addressing is a prerequisite for many instances of quantum information processing. We demonstrate this capability on trapped-ion qubits with microwave near fields delivered by electrode structures integrated into a microfabricated surface-electrode trap. We describe four approaches that may be used in quantum information experiments with hyperfine levels as qubits. We implement individual control on two 25Mg+ ions separated by 4.3 μm and find spin-flip crosstalk errors on the order of 10(-3).

DOI
10.1103/physrevlett.110.173002

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Bulletin of the American Physical Society•May 24, 2016•0 citations
Individual-qubit addressing is a prerequisite for many instances of quantum information processing. We demonstrate this capability on trapped-ion qubits with microwave near fields delivered by electrode structures integrated into a microfabricated surface-electrode trap. We describe four approaches that may be used in quantum information experiments with hyperfine levels as qubits. We implement individual control on two 25Mg+ ions separated by 4.3 μm and find spin-flip crosstalk errors on the order of 10(-3).
A dense array of ions in microfabricated traps represents one possible way to scale up ion trap quantum computing. The ability to address individual ions is an important component of such a scheme. We demonstrate individual addressing of trapped ions in a microfabricated surface-electrode trap using a magnetic field gradient generated on-chip. A frequency splitting of 310(2) kHz for two ions separated by 5 μm is achieved. Selective single qubit operations are performed on one of two trapped ions with an average of 2.2(±1.0%) crosstalk. Coherence time is reduced by the magnetic field gradient, but the spin-echo technique effectively restores the coherence time.
This thesis reports high-fidelity near-field spatial microwave addressing of long-lived 43Ca+ "atomic clock" qubits performed in a two-zone single-layer surface-electrode ion trap. Addressing is implemented by using two of the trap's integrated microwave electrodes, one in each zone, to drive single-qubit rotations in the zone we choose to address whilst interferometrically cancelling the microwave field at the neighbour (non-addressed) zone. Using this field-nulling scheme, we measure a Rabi frequency ratio between addressed and non-addressed zones of up to 1400, from which we calculate an addressing error (or a spin-flip probability on the qubit transition) of 1e-6. Off-resonant excitation out of the qubit state is a more significant source of error in this experiment, but we also demonstrate polarisation control of the microwave field at an error level of 2e-5, which, if combined with individual-ion addressing, would be sufficient to suppress off-resonant excitation errors to the 1e-9 level. Further, this thesis presents preliminary results obtained with a micron-scale coupled-microstrip differential antenna probe that can be scanned over an ion-trap chip to map microwave magnetic near fields. The probe is designed to enable the measurement of fields at tens of microns above electrode surfaces and to act as an effective characterisation tool, speeding up design-fabrication-characterisation cycles in the production of new prototype microwave ion-trap chips. Finally, a new multi-layer design for an ion-trap chip which displays, in simulations, a 100-fold improvement in addressing performance, is presented. The chip electrode structure is designed to use the cancelling effect of microwave return currents to produce Rabi frequency ratios of order 1000 between trap zones using a single microwave electrode (i.e. without the need for nulling fields). If realised, this chip could be used to drive individually addressed single-qubit operations on arrays of memory qubits in parallel and with high fidelity.
Individual addressing of qubits is essential for scalable quantum computation. Spatial addressing allows unlimited numbers of qubits to share the same frequency, while enabling arbitrary parallel operations. We demonstrate addressing of long-lived 43Ca+^{43}\mathrm{Ca}^{+}43Ca+ ``atomic clock'' qubits held in separate zones ($960\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\text{m}$ apart) of a microfabricated surface trap with integrated microwave electrodes. Such zones could form part of a ``quantum charge-coupled device'' architecture for a large-scale quantum information processor. By coherently canceling the microwave field in one zone we measure a ratio of Rabi frequencies between addressed and nonaddressed qubits of up to 1400, from which we calculate a spin-flip probability on the qubit transition of the nonaddressed ion of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Off-resonant excitation then becomes the dominant error process, at around $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. It can be prevented either by working at higher magnetic field, or by polarization control of the microwave field. We implement polarization control with error $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, which would suffice to suppress off-resonant excitation to the $\ensuremath{\sim}{10}^{\ensuremath{-}9}$ level if combined with spatial addressing. Such polarization control could also enable fast microwave operations.
We describe the design, fabrication, and testing of a surface-electrode ion trap, which incorporates microwave waveguides, resonators, and coupling elements for the manipulation of trapped ion qubits using near-field microwaves. The trap is optimised to give a large microwave field gradient to allow state-dependent manipulation of the ions' motional degrees of freedom, the key to multi-qubit entanglement. The microwave field near the centre of the trap is characterised by driving hyperfine transitions in a single laser-cooled 43Ca+ ion.
Individual addressing of qubits is essential for scalable quantum computation. Spatial addressing allows unlimited numbers of qubits to share the same frequency, whilst enabling arbitrary parallel operations. We demonstrate addressing of long-lived 43Ca+^{43}\text{Ca}^+43Ca+ atomic clock qubits held in separate zones of a microfabricated surface trap with integrated microwave electrodes. By coherently cancelling the microwave field in one zone we measure a ratio of Rabi frequencies between addressed and non-addressed qubits of up to 1400, implying an addressing error of 1.3×10−61.3\times 10^{-6}1.3×10−6. Off-resonant excitation prevents this error level being directly demonstrated, but we also show polarization control of the microwave field with error 2×10−52\times 10^{-5}2×10−5, sufficient to suppress off-resonant excitation out of the qubit states to the ∼10−9\sim 10^{-9}∼10−9 level. Such polarization control could enable fast microwave operations.
High-fidelity spatial addressing of 43Ca+^{43}\text{Ca}^+43Ca+ qubits using near-field microwave control
Individual addressing of qubits is essential for scalable quantum computation. Spatial addressing allows unlimited numbers of qubits to share the same frequency, whilst enabling arbitrary parallel operations. We demonstrate addressing of long-lived 43Ca+^{43}\text{Ca}^+43Ca+ atomic clock qubits held in separate zones of a microfabricated surface trap with integrated microwave electrodes. By coherently cancelling the microwave field in one zone we measure a ratio of Rabi frequencies between addressed and non-addressed qubits of up to 1400, implying an addressing error of 1.3×10−61.3\times 10^{-6}1.3×10−6. Off-resonant excitation prevents this error level being directly demonstrated, but we also show polarization control of the microwave field with error 2×10−52\times 10^{-5}2×10−5, sufficient to suppress off-resonant excitation out of the qubit states to the ∼10−9\sim 10^{-9}∼10−9 level. Such polarization control could enable fast microwave operations.