Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session M5: Quantum Gates and Networks |
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Chair: Martin Lichtman, University of Wisconsin Room: Fairfield |
Thursday, June 11, 2015 8:00AM - 8:12AM |
M5.00001: Implementation of Universal-Not Gate on an Embedding Quantum System with a Trapped Ion Kuan Zhang, Xiang Zhang, Jiajun Ma, Mile Gu, Kihwan Kim, Jayne Thompson, Vlatko Vedral Quantum version of Universal-Not (U-Not) gate, that transforms any qubit state into its orthogonal counterpart, is principally forbidden by quantum mechanics. Here, we use an embedding scheme that encodes each qubit within an extended Hilbert space, to emulate the effect of implementing a U-Not gate on an arbitrary qubit state. This enables us to emulate antiunitary operations such as complex conjugation [1,2]. Strikingly, in the presence of U-Not gate the mutual information between two qubit systems can be increased or decreased by local operations. First, we prepare two qubits in the same state, where one is in internal degree of freedom and the other is in motional mode of a 171Yb+ ion. After applying the U-Not gate to the internal qubit, indeed, we observe that the mutual information has changed. \\[4pt] [1] J. Casanova, et al., Phys. Rev. X 1, 021018 (2011).\\[0pt] [2] X. Zhang, et al., arXiv:1409.3681 (2014). [Preview Abstract] |
Thursday, June 11, 2015 8:12AM - 8:24AM |
M5.00002: High-fidelity single-shot Toffoli gate via quantum control Barry Sanders, Ehsan Zahedinejad, Joydip Ghosh A single-shot Toffoli, or controlled-controlled-NOT, gate is desirable for classical and for quantum information processing. The Toffoli gate alone is universal for reversible computing and, accompanied by the Hadamard gate, are universal for quantum computing. The Toffoli gate is a key ingredient for (non-topological) quantum error correction. Currently Toffoli gates are achieved by decomposing into sequentially implemented single- and two-qubit gates, which requires much longer times and yields lower overall fidelities compared to a single-shot implementation. We develop a quantum-control procedure to directly construct single-shot Toffoli gates and devise a scheme for three nearest-neighbor-coupled superconducting transmon systems that should operate with 99.9{\%} fidelity under realistic conditions. The gate is achieved by a non-greedy quantum control procedure using our enhanced version of the Differential Evolution algorithm. arXiv:1501.04676 [Preview Abstract] |
Thursday, June 11, 2015 8:24AM - 8:36AM |
M5.00003: Rydberg blockade of atomic ensemble qubits Minho Kwon, Matt Ebert, Dahan Kim, Thad Walker, Mark Saffman We demonstrate \textbar W\textgreater state encoding of multi-atom ensemble qubits. Using optically trapped Rb atoms the T2 coherence time is 2.6(3) ms for an average ensemble number of N $=$ 7.6 atoms and scales approximately inversely with N. Strong Rydberg blockade between two ensemble qubits is demonstrated with a fidelity of 0.89(1) and a fidelity of $\sim $1.0 when postselected on control ensemble excitation. We will present progress towards entanglement of two ensemble qubits using the Rydberg blockade interaction. [Preview Abstract] |
Thursday, June 11, 2015 8:36AM - 8:48AM |
M5.00004: Single qubit gates on neutral atoms in a 3d Optical lattice Aishwarya Kumar, Yang Wang, Xianli Zhang, Theodore A. Corcovilos, David S. Weiss Neutral atoms are especially promising candidates for quantum computing because of their inherent scalability. To realize this scalability requires being able to manipulate the quantum information at target qubits with high fidelity and low crosstalk. We will present two single qubit gate addressing protocols. We have experimentally applied them both to targeted sites in a 5x5x5 3D array. The two distinct approaches both use crossed MEMS-mirror directed addressing beams along with microwave pulses to target atoms at single sites, while having minimal impact on the quantum information at non-target sites. [Preview Abstract] |
Thursday, June 11, 2015 8:48AM - 9:00AM |
M5.00005: Quantum Information Processing with Modular Networks Clayton Crocker, Ismail V. Inlek, David Hucul, Ksenia Sosnova, Grahame Vittorini, Chris Monroe Trapped atomic ions are qubit standards for the production of entangled states in quantum information science and metrology applications. Trapped ions can exhibit very long coherence times, external fields can drive strong local interactions via phonons, and remote qubits can be entangled via photons. Transferring quantum information across spatially separated ion trap modules for a scalable quantum network architecture relies on the juxtaposition of both phononic and photonic buses. We report the successful combination of these protocols within and between two ion trap modules on a unit structure of this architecture where the remote entanglement generation rate exceeds the experimentally measured decoherence rate. Additionally, we report an experimental implementation of a technique to maintain phase coherence between spatially and temporally distributed quantum gate operations, a crucial prerequisite for scalability. Finally, we discuss our progress towards addressing the issue of uncontrolled cross-talk between photonic qubits and memory qubits by implementing a second ion species, Barium, to generate the photonic link. [Preview Abstract] |
Thursday, June 11, 2015 9:00AM - 9:12AM |
M5.00006: Building a quantum processor using photons and atoms Eden Figueroa Barragan, Mehdi Namazi, Bertus Jordaan, Samuel Rind, Connor Kupchak Given the recent experimental success in regard to the advancement of quantum devices, we are now at the point where we must interconnect many of them in order to bring about the first generation of quantum processing machines. In this elementary quantum processor, individual nodes must be equipped with the functionality to perform several key tasks in order to meet the criteria necessary for quantum information processing. Namely, some nodes need to be able to receive, store and retrieve photonic qubits (quantum memories), while other nodes must be geared toward the manipulation of qubits (quantum gates). In this work we will present our progress regarding the construction of a many-device quantum processor capable of storing and processing photonic polarization qubits. We will discuss our recent experiments in which we have tested the feasibility of using room temperature ensembles as a node to process quantum information, by performing coherent state quantum process tomography (csQPT) of an optically-induced phase shift in a electromagnetically induced transparency N-type atomic medium. Moreover, we will also present our recent experiment in which we have explored the interconnection of several quantum devices by cascading the storage processes of two room temperature single-photon level polarization qubit memories. [Preview Abstract] |
Thursday, June 11, 2015 9:12AM - 9:24AM |
M5.00007: Preserving photon qubits in an unknown quantum state with Knill Dynamical Decoupling -- Towards an all optical quantum memory Manish K. Gupta, Erik J. Navarro, Todd A. Moulder, Jason D. Mueller, Ashkan Balouchi, Katherine L. Brown, Hwang Lee, Jonathan P. Dowling The storage of quantum states and its distribution over long distances is essential for emerging quantum technologies such as quantum networks and long distance quantum cryptography. The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates in a single mode fiber, to minimize decoherence of polarization qubit and show that a fidelity greater than $99\%$ can be achieved in absence of rotation error and fidelity greater than $96\%$ can be achieved in presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum memory, quantum delay line, and quantum repeater. [Preview Abstract] |
Thursday, June 11, 2015 9:24AM - 9:36AM |
M5.00008: Multiplexing OAM states in an optical fiber: Increase bandwidth of quantum communication and QKD applications Manish Kumar Gupta, Jonathan P. Dowling We propose a noble method for multiplexing OAM states to increase bandwidth of communication in a birefringent single-mode optical fiber for quantum communication and QKD applications by minimizing the decoherence. We analytically derive and show that the rate of decoherence for OAM state in a birefringent optical fiber is proportional to $l^2$. We also show numerically that decoherence can be minimized with CPMG pulse sequence to preserve the state with $>90\%$ fidelity for smaller values of $l$ to allow for high-bandwidth communication. [Preview Abstract] |
Thursday, June 11, 2015 9:36AM - 9:48AM |
M5.00009: High Data Rate Quantum Cryptography Paul Kwiat, Bradley Christensen, Kevin McCusker, Daniel Kumor, Daniel Gauthier While quantum key distribution (QKD) systems are now commercially available, the data rate is a limiting factor for some desired applications (e.g., secure video transmission). Most QKD systems receive at most a single random bit per detection event, causing the data rate to be limited by the saturation of the single-photon detectors. Recent experiments have begun to explore using larger degree of freedoms, i.e., temporal or spatial qubits, to optimize the data rate. Here, we continue this exploration using entanglement in multiple degrees of freedom. That is, we use simultaneous temporal and polarization entanglement to reach up to 8.3 bits of randomness per coincident detection. Due to current technology, we are unable to fully secure the temporal degree of freedom against all possible future attacks; however, by assuming a technologically-limited eavesdropper, we are able to obtain 23.4 MB/s secure key rate across an optical table, after error reconciliation and privacy amplification. In this talk, we will describe our high-rate QKD experiment, with a short discussion on our work towards extending this system to ship-to-ship and ship-to-shore communication, aiming to secure the temporal degree of freedom and to implement a 30-km free-space link over a marine environment. [Preview Abstract] |
Thursday, June 11, 2015 9:48AM - 10:00AM |
M5.00010: Low Noise Quantum Frequency Conversion from Rb Wavelengths to Telecom O-band Xiao Li, Neal Solmeyer, Daniel Stack, Qudsia Quraishi Ideal quantum repeaters would be composed of long-lived quantum memories entangled with flying qubits. They are becoming essential elements to achieve quantum communication over long distances in a quantum network. However, quantum memories based on neutral atoms operate at wavelengths in the near infrared, unsuitable for long distance communication. The ability to coherently convert photons entangled with quantum memories into telecom wavelengths reduces the transmission loss in optical fibers and therefore dramatically improves the range of a quantum repeater. Furthermore, quantum frequency conversion (QFC) can enable entanglement and communication between different types of quantum memories, thus creating a versatile hybrid quantum network. A recent experiment has shown the conversion of heralded photons from Rb-based memories to the telecom C-band [Nat. Commun. \textbf{5}, 3376]. We implement a setup using a nonlinear PPLN waveguide for the QFC into a wavelength region where the noise-floor would be limited by dark counts rather than pump photons. Our approach uses a pump laser at a much longer wavelength. It has the advantage that the strong pump itself and the broad background in the PPLN can be nearly completely filtered from the converted signal. Such low background level allows for the conversion to be done on the heralding photon, which enables the generated entanglement to be used in a scalable way to multiple nodes remotely situated and to subsequent protocols. [Preview Abstract] |
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