C ○ rinton press high-fidelity quantum control using ion crystals in a penning trap (906).

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Author	Michael J. Biercuk, A. Hermann Uys, B. Vandevender, Aaron P.
Abstract	We provide an introduction to the use of ion crystals in a Penning trap [1, 2, 3, 4] for experiments in quantum information. Macroscopic Penning traps allow for the containment of a few to a few million atomic ions whose internal states may be used in quantum information experiments. Ions are laser Doppler cooled [1], and the mutual Coulomb repulsion of the ions leads to the formation of crystalline arrays [5, 6, 7, 8]. The structure and dimensionality of the resulting ion crystals may be tuned using a combination of control laser beams and external potentials [9, 10]. We discuss the use of two-dimensional 9 Be + ion crystals for experimental tests of quantum control techniques. Our primary qubit is the 124 GHz ground-state electron spin flip transition, which we drive using microwaves [11, 12]. An ion crystal represents a spatial ensemble of qubits, but the effects of inhomogeneities across a typical crystal are small, and as such we treat the ensemble as a single effective spin. We are able to initialize the qubits in a simple state and perform a projective measurement [1] on the system. We demonstrate full control of the qubit Bloch vector, performing arbitrary highfidelity rotations (τπ ∼200 µs). Randomized Benchmarking [13] demonstrates an error per gate (a Pauli-randomized π/2 and π pulse pair) of 8 ± 1 × 10 −4. Ramsey interferometry and spin-locking [14] measurements are used to elucidate the limits of qubit coherence in the system, yielding a typical free-induction decay coherence time of T2 ∼2 ms, and a limiting T1ρ ∼688 ms. These experimental specifications make ion crystals in a Penning trap ideal candidates for novel experiments in quantum control. As such, we briefly describe recent efforts aimed at studying the error-suppressing capabilities
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Subject Keyword	Ion Crystal Penning Trap Typical Crystal Describe Recent Effort Quantum Control Mutual Coulomb Repulsion Quantum Information Quantum Information Experiment Spatial Ensemble Limiting T1 Full Control Primary Qubit Experimental Specification Laser Doppler Single Effective Spin Experimental Test Simple State Crystalline Array Atomic Ion Penning Trap Ideal Candidate Qubit Bloch Vector Typical Free-induction Decay Coherence Time Novel Experiment External Potential Qubit Coherence Ramsey Interferometry Internal State Quantum Control Technique Control Laser Beam Error-suppressing Capability Arbitrary Highfidelity Rotation Projective Measurement
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