Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session H09: Quantum Gates 
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Chair: John Bollinger, NIST Room: Grand H 
Wednesday, May 30, 2018 8:00AM  8:12AM 
H09.00001: Robust entanglement of trapped ion qubits Yotam Shapira, Ravid Shaniv, Tom Manovitz, Nitzan Akerman, Roee Ozeri Twoqubit entangling gates are central to quantum information processing. High fidelity twoqubit entangling gates have been demonstrated in several trapped ions systems. A common choice for such entangling gates is the wellknown bichromatic MølmerSørensen (MS) gate, which ideally allows for deterministic twoqubit entanglement. However, calibration errors such as gatetiming errors or drifts of the normalmode harmonic frequency result in a, temperaturesensitive, reduced gate fidelity. Furthermore, the gate is constrained to act slower than the trapping frequency due to offresonance direct carrier coupling. Here, we generalize the MS gate by driving the ions with a multichromatic drive, the different components of the drive are then treated as additional degrees of freedom that allow for reducing or eliminating different error mechanisms leading to robust entanglement. Specifically we implement our robust entanglement scheme on two trapped $^{88}\text{Sr}^{+}$ ions. We explicitly measure the increased robustness to gatetiming errors, normalmode frequency errors and offresonance carrier coupling. [Preview Abstract] 
Wednesday, May 30, 2018 8:12AM  8:24AM 
H09.00002: Entanglement between two species of atomic ions and the loopholefree test of quantum contextuality Pengfei Wang, Junhua Zhang, Mark Um, Ye Wang, Tian Xie, Naijun Jin, JingNing Zhang, Kihwan Kim We report the entanglement between $^{171}$Yb$^+$ ion and $^{138}$Ba$^+$ ion. First, we prepare all the motional state to near the groundstate by the threestage cooling of Doppler, the EIT and the sideband cooling on Ba$^+$ ion. Then, we apply the Raman laser beams of 355 nm for Yb$^+$ and 532 nm for Ba$^+$ and create the entanglement of the two ions through a M$\o$lmerS$\o$rensen interaction. We detect the quantum states of $^{171}$Yb$^+$ and $^{138}$Ba$^+$ by the standard fluorescence scheme. For the $^{138}$Ba$^+$ ion, we shelve an electronic state in S$_{1/2}$ to a state in D$_{5/2}$ by applying a narrowlinewidth laser of 1762 nm. With the entanglement between two species of atomic ions, we can experimentally verify the quantum contexuality without the major loopholes of detection and compatibility. In our experimental realization, it is naturally free of the detection loophole, since the detection efficiencies of both ions are over 98 $\%$. It is also free of the compatibility loophole, since we measure the pairs of the joint observables simultaneously instead of the sequential measurements with totally different wavelength of laser beams for each ion. [Preview Abstract] 
Wednesday, May 30, 2018 8:24AM  8:36AM 
H09.00003: Entangling Ions through Multiple Transverse Modes on an IonChain Kuan Zhang, Yao Lu, Shuaining Zhang, Yangchao Shen, Wentao Chen, JingNing Zhang, Kihwan Kim A GreenbergerHorneZeilinger (GHZ) state of up to 14 ions has been created by applying a single operation of M\o{}lmerS\o{}rensen (MS) gate~[1,2]. In their gate, it is essential to use only the centermass (CM) mode along the axial direction, therefore, requiring well isolation of the mode from all the other motional modes. However, it is difficult to maintain the requirement when the number of ions further increases in a linear ionchain with reasonable trap frequencies. Here, we present a scalable multiqubit gate, which entangles ions by using multiple transverse modes instead of a single CM mode. Our gate considers the influence of all the motional modes, and creates entanglement among arbitrary number of selected ions in the ionchain by simultaneously applying laser beams to them. Our multiqubit gate provides an efficient and scalable solution for trappedion quantum computation and simulation. [1] Anders S\o{}rensen and Klaus M\o{}lmer. Phys.~Rev.~Lett. 62, 022311 (2000). [2] Thomas~Monz, et al., Phys.~Rev.~Lett. 106, 130506 (2011). [Preview Abstract] 
Wednesday, May 30, 2018 8:36AM  8:48AM 
H09.00004: Parallel 2Qubit Operations on a Programmable Ion Trap Quantum Computer Caroline Figgatt, Aaron Ostrander, Norbert Linke, Kevin Landsman, Daiwei Zhu, Dmitri Maslov, Christopher Monroe Performing parallel operations will be a powerful capability as deeper circuits on larger, more complex quantum computers present new challenges. We present experimental results for a pair of 2qubit gates performed simultaneously in a single chain of trapped ions. The system used is a programmable quantum computer consisting of a linear chain of five trapped $^{171}$Yb$^+$ atomic clock ions with long coherence times. We employ a pulse shaping scheme that modulates the phase and amplitude of the Raman transitions to drive programmable highfidelity 2qubit XX gates in parallel by coupling to the collective modes of motion of the ion chain. Ensuring the interaction produced yields only spinspin interactions between the desired pairs with neither residual spinmotion entanglement nor “crosstalk” spinspin entanglement is a nonlinear constraint problem, and pulse solutions are found using optimization techniques. As an application, we demonstrate the quantum full adder [1] using a depth4 circuit requiring the use of parallel 2qubit operations [2] as well as modular 1 and 2qubit operations previously demonstrated on this system [3]. [1] Opt. News, 11, 11–20 (1985), [2] IEEE Trans. Comput.Aided Design Integr. Circuits Syst., 27(3):436444 (2008), [3] Nature 536, 63 (2016). [Preview Abstract] 
Wednesday, May 30, 2018 8:48AM  9:00AM 
H09.00005: Entanglement of trapped ions using lowfrequency magnetic field gradients Shaun C. Burd, David T. C. Allcock, Raghavendra Srinivas, Daniel H. Slichter, Andrew Wilson, Dietrich Leibfried, David Wineland Entangled states of trapped ions are typically generated using laserinduced spinmotion coupling. Spinmotion coupling with hyperfine qubits has also been demonstrated with microwave magnetic fields instead of lasers, thus eliminating photon scattering errors and offering potential benefits for scalability. These experiments have relied on either static magnetic field gradients or oscillating magnetic field gradients at GHz frequencies[14]. We present a method of spinmotion coupling using a magnetic field gradient oscillating at MHz frequencies. We describe progress in using this method to perform one and twoqubit manipulations of $^{25}$Mg$^{+}$ ions in a cryogenic microfabricated surfaceelectrode trap. This implementation offers important technical advantages over both the staticgradient and GHzgradient techniques. [1] Mintert and Wunderlich PRL 87, 257904 (2001) [2] Weidt et al. PRL 117, 220501 (2016) [3] Ospelkaus et al. Nature 476, 181 (2011) [4] Harty et al. PRL 117, 140501 (2016) [Preview Abstract] 
Wednesday, May 30, 2018 9:00AM  9:12AM 
H09.00006: Trapped ioninspired entangling gate for superconducting qubits Sydney Schreppler, Marie Lu, Lukas Buchmann, Felix Motzoi, Irfan Siddiqi Quantum simulators of analog and digital varieties rely on the ability to entangle constituent particles with high fidelity. The M{\o}lmerS{\o}rensen gate underlies much of the success of trappedion qubits, allowing for twoqubit entanglement with fidelity greater than 99{\%} and for simultaneous multiqubit operations. For the ions, qubitqubit entanglement is achieved via stimulated Raman transitions and through their interaction with a shared phonon mode. We describe the development of a M{\o}lmerS{\o}rensen inspired gate for superconducting qubits, employing an analogous shared photon mode and a bichromatic driving field to engineer multiqubit entanglement. This new functionality encourages development of hybrid analogdigital approaches to quantum simulations with superconducting qubit systems. [Preview Abstract] 
Wednesday, May 30, 2018 9:12AM  9:24AM 
H09.00007: Photonmediated universal quantum gate between two neutral atoms in an optical cavity Stephan Welte, Bastian Hacker, Severin Daiss, Stephan Ritter, Lin Li, Gerhard Rempe Optical highfinesse resonators provide an efficient interface between flying photonic qubits and stationary matter qubits [1] in a future quantum network for secure quantum communication and distributed quantum computing. A prerequisite for the construction of a scalable network is that each node contains several qubits that are connected through universal quantum gate operations. We experimentally realized [2] such a gate [3] between two neutral Rubidium atoms strongly coupled to an optical resonator. The gate is mediated by one optical photon propagating in the network channel defined by the resonator mode. The reflection of the photon from the resonator creates an interaction that is independent of the interatomic distance. We demonstrate the functionality of our gate as a CNOT as well as its ability to maximally entangle two atoms. The presented gate mechanism has the potential to serve in an entanglement swapping protocol to generate entanglement over large distances in a quantum repeater. [1] A. Reiserer, G. Rempe, Rev. Mod. Phys. 87, 1379 (2015). [2] S. Welte, B. Hacker, S. Daiss, S. Ritter, G. Rempe, arXiv 1801.05980 (2018). [3] L.M. Duan, B. Wang, H. J. Kimble, Phys. Rev. A 72, 032333 (2005). [Preview Abstract] 
Wednesday, May 30, 2018 9:24AM  9:36AM 
H09.00008: Quantum compilation optimized for experiments with multiqubit gates Liangyu Ding, Xiang Zhang, Qiuxin Zhang, Danna Shen, Xiran Sun, Wei Zhang There is increasing interest in implementing quantum algorithms via simpler and shorter experimental operations for building universal quantum computers. Here, we present a general quantum computation compiler, which maps arbitrary quantum algorithm to an optimal quantum circuit consisting of a sequential set of universal gates which is feasible to operate directly in experiment with atomic qubits by lasers. We implement several methods, including matrix elementary decomposition, cosinesine decomposition, quantum Shannon decomposition and Cartan's KAK decomposition, to transform the quantum algorithm into a series of onebit gates and specific twobit or multibit gates. The compiler optimizes experimental gate sequence by heuristically applying mirroring and merging tricks. Moreover, we use algebraic decomposition and numerical optimization method to compile unitaries using native multibit gates, i.e., Ising gates, which significantly reduce gate numbers. The compilation technique is practically favorable and will be used in our following trapped ions experiment. [Preview Abstract] 
Wednesday, May 30, 2018 9:36AM  9:48AM 
H09.00009: A PhotonPhoton Quantum Gate Based on Rydberg Polaritons Steffen SchmidtEberle, Daniel Tiarks, Thomas Stolz, Stephan Duerr, Gerhard Rempe Rydberg polaritons offer a unique way to create strong interactions for photons. We utilize these interactions to demonstrate a photonphoton quantum gate. To achieve this, a photonic control qubit is stored in a quantum memory consisting of a superposition of a ground state and a Rydberg state in an ultracold atomic gas. This qubit interacts with a photonic target qubit in the form of a propagating Rydberg polariton to generate a conditional pi phase shift.\footnote{D. Tiarks et al., Science Advances 2, 1600036 (2016)} Finally, the control photon is retrieved. We measure two controlledNOT truth tables and the twophoton state after an entanglinggate operation. This work is an important step toward applications in optical quantum information processing, such as deterministic photonic Bellstate detection which is crucial for quantum repeaters. [Preview Abstract] 

H09.00010: ABSTRACT WITHDRAWN 
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