Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session M8: Quantum Control and TomographyInvited

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Chair: Wes Campbell, University of California, Los Angeles Room: 314 
Thursday, June 8, 2017 8:00AM  8:30AM 
M8.00001: Highfidelity operations in microfabricated surface ion traps Invited Speaker: Peter Maunz Trapped ion systems can be used to implement quantum computation as well as quantum simulation. To scale these systems to the number of qubits required to solve interesting problems in quantum chemistry or solid state physics, the use of large multizone ion traps has been proposed [1]. Microfabrication enables the realization of surface electrode ion traps with complex electrode structures. While these traps may enable the scaling of trapped ion quantum information processing (QIP), microfabricated ion traps also pose several technical challenges. Here, we present Sandia's trap fabrication capabilities and characterize trap properties and shuttling operations in our most recent high optical access trap (HOA2). To demonstrate the viability of Sandia's microfabricated ion traps for QIP we realize robust single and twoqubit gates and characterize them using gate set tomography (GST). In this way we are able to demonstrate the first single qubit gates [2] with a diamond norm of less than $1.7 \times 10^{4}$, below a rigorous fault tolerance threshold for general noise of $6.7 \times 10^{4}$ [3]. Furthermore, we realize M\o lmerS\o rensen two qubit gates with a process fidelity of $99.58(6)\%$ also characterized by GST. These results demonstrate the viability of microfabricated surface traps for state of the art quantum information processing demonstrations. [1] D. Kielpinski, C. Monroe, and D. J. Wineland, Nature 417, 709 (2002). [2] R. BlumeKohout et al. arXiv:1606.07674. [3] P. Aliferis and J. Preskill, Phys. Rev. A 79, 012332 (2009). [Preview Abstract] 
Thursday, June 8, 2017 8:30AM  9:00AM 
M8.00002: Quantum computing with atoms in a 3D optical lattice: addressing and sorting atoms Invited Speaker: David Weiss Trapping longlived neutral atom qubits in a 3D optical lattice will ultimately allow their entanglement with many near neighbors. To date, we have prepared 50 single atoms near the ground states of their lattice sites, and have demonstrated high fidelity single qubit addressing at each site, with minimal crosstalk despite the challenges of the 3D geometry [Y. Wang, A. Kumar, T.Y. Wu {\&} D.S. Weiss, \textit{Science }\textbf{352}, 15621565 (2016)]. I will describe this work, and explain how we are going about sorting the atoms in 3D to generate arbitrary occupancy patterns, the next step before entangling nearby pairs of atoms. [Preview Abstract] 
Thursday, June 8, 2017 9:00AM  9:30AM 
M8.00003: Practical applications of compressed sensing in quantum state tomography~ Invited Speaker: Carlos Riofrio As quantum systems get closer to technological applications, the problem of identifying, certifying, and characterizing them becomes more daunting. In fact, a complete characterization of a quantum system requires determining a number of parameters that grow exponentially with the system size. New paradigms that allow for efficient signal processing must be developed and tested to overcome this roadblock. In this talk, we present an overview of the most recent developments in quantum state tomography via compressed sensing. We show a complete analysis based on experimental data from two different systems: First, a photonic circuit that prepares highly entangled photons corresponding to 4qubit states, which we use as a testbed to showcase our tomographic procedure in a variety of scenarios; Second, a 7qubit system of trapped ions which encodes a single logical qubit via a color code, in which highly incomplete data is observed. We show how compressed sensing and model selection ideas can be combined in practice.~ [Preview Abstract] 
Thursday, June 8, 2017 9:30AM  10:00AM 
M8.00004: Arbitrary DickeState Control of Symmetric Rydberg Ensembles Invited Speaker: Ivan Deutsch We study the production of arbitrary superpositions of Dicke states via optimal control. We show that N atomic hyperfine qubits, interacting symmetrically via the Rydberg blockade, are well described by the JaynesCummings Model (JCM), familiar in cavity QED. In this isomorphism, the presence or absence of a collective Rydberg excitation plays the role of the twolevel system and the number of symmetric excitations of the hyperfine qubits plays the role of the bosonic excitations of the JCM. This system is fully controllable through the addition of phasemodulated microwaves that drive transitions between the Rydbergdressed states. In the weak dressing regime, this results in a singleaxis twisting Hamiltonian, plus timedependent rotations of the collective spin. For strong dressing we control the entire JaynesCummings ladder. Using optimal control, we design microwave waveforms that can generate arbitrary states in the symmetric subspace. This includes cat states, Dicke states, and spin squeezed states. With currently feasible parameters, it is possible to generate arbitrary symmetric states of \textunderscore 10 hyperfine qubits in \textasciitilde 1 microsec, assuming a fast microwave phase switching time. The same control can be achieved with a ``dressedground control'' scheme, which reduces the demands for fast phase switching at the expense of increased total control time. More generally, we can achieve control on larger ensembles of qubits by designing waveforms that are bandwidth limited within the coherence time of the system. We use this to study general questions of the ``quantum speed limit'' and information content in a waveform that is needed to generate arbitrary quantum states. [Preview Abstract] 
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