Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C27: Quantum Computing, Quantum Algorithms, and Quantum Simulation 
Hide Abstracts 
Sponsoring Units: GQI Chair: Alan AspuruGuzik, Harvard University Room: 329 
Monday, March 18, 2013 2:30PM  2:42PM 
C27.00001: Quantum Computing through Quantum Networks Cheng Wu Entanglement of two AharonovBohm (AB) rings, or two artificial atoms, is similar to the entanglement of spins from two electrons. The directions of the angular momentum of two AB rings serve as the inputs for a basic twobit computing in the quantum network. The question is whether the readout is to be performed under a short and weak external perturbation? We found that a stronger entanglement than the situation needed for a quantum superposition combines with a strong external terminal connections is the only solution for robust classical readouts. A ``halfadder'' example will be presented. There has to be an interrelation between internal and external coupling strengths. They are so adjusted for each other so that readouts are possible. [Preview Abstract] 
Monday, March 18, 2013 2:42PM  2:54PM 
C27.00002: Analytically solvable driven timedependent twolevel quantum systems Edwin Barnes, Sankar Das Sarma Analytical solutions to the timedependent Schrodinger equation describing a driven twolevel system are invaluable to many areas of physics, but they are also extremely rare. Here, we present a simple algorithm based on a type of partial reverseengineering that generates an unlimited number of exact analytical solutions for a general timedependent Hamiltonian. We demonstrate this method by presenting several new exact solutions that are particularly relevant to qubit control in quantum computing applications. We further show that our formalism easily generates analytical control protocols for performing sweeps across energy level anticrossings that execute perfect LandauZener interferometry and rapid adiabatic passage near the quantum speed limit. [1] Phys. Rev. Lett. 109, 060401 (2012) [Preview Abstract] 
Monday, March 18, 2013 2:54PM  3:06PM 
C27.00003: Compilted Quantum Factoring Circuits Omar Gamel, Daniel James Shor's factoring algorithm is held as one of the most promising and useful applications of quantum computing. It allows one to factor large numbers in polynomial time, undermining the most common cryptographic schemes in use today, such as RSA cryptography. The well known algorithm is based on the quantum fourier transform to find the period of a function, and also makes heavy use of the modular exponentiation operation, given by, \begin{equation} U:a0 \rightarrow ax^a(mod N), \end{equation} where $N$ is the number to be factored, and $x$ is a random positive integer coprime with $N$. The modular exponentiation is the bottleneck of the algorithm, the portion that uses the most time. The generic algorithm can factorize any $N$ in time order $(\log{N})^3$, assuming sufficient memory space for intermediate calculations. Reducing the memory available (as long as it still lies above a certain threshold) increases the time taken by multiplicative factors, keeping its order the same in $\log(N)$. However, for a given $N$, or class of $N$'s to factorize, the generic algorithm may be suboptimal, and can be optimized to result in substantial savings in both memory needed and operation time. The different suboperations involved in modular exponentiat [Preview Abstract] 
Monday, March 18, 2013 3:06PM  3:18PM 
C27.00004: Quantum Algorithm for Solving an NPComplete Problem Hefeng Wang, Fuli Li When a probe qubit is coupled to a quantum register that represents a physical system, the probe qubit will exhibit a dynamical response only when it is resonant with a transition in the system. Using this principle, we propose a quantum algorithm for solving a specific NPcomplete problem, the 3bit Exact Cover problem, EC3. We show that on a quantum computer, the number of qubits increases linearly with the size of the EC3 problem, while the efficiency of the algorithm is independent of the size of the problem. Our results indicate that quantum computers may be able to outperform classical computers in solving NPcomplete problems. [Preview Abstract] 
Monday, March 18, 2013 3:18PM  3:30PM 
C27.00005: Quantum Steering as a Quantum Game Sai Vinjanampathy, JingLing Chen, Mile Gu, L.C. Kwek "Steerable states" are a subset of entangled states, that contain in them the set of Bell nonlocal states. A bipartite state shared by Alice and Bob is called steerable if by performing measurements, the ensemble that Alice can produce on Bob's side is unexplained by any local hidden variable theory. We will provide an operational interpretation of quantum steering by proposing a quantum game. The probability that the players win this game will be related to quantum steering. Furthermore, we will show how the various hierarchies between entanglement, steering and Bell nonlocality are preserved by this quantum game. [Preview Abstract] 
Monday, March 18, 2013 3:30PM  3:42PM 
C27.00006: Quantum Data Fitting Nathan Wiebe We provide a new quantum algorithm that efficiently determines the quality of a leastsquares fit over an exponentially large data set by building upon an algorithm for solving systems of linear equations efficiently (Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)). In many cases, our algorithm can also efficiently find a concise function that approximates the data to be fitted and bound the approximation error. In cases where the input data is a pure quantum state, the algorithm can be used to provide an efficient parametric estimation of the quantum state and therefore can be applied as an alternative to full quantum state tomography given a fault tolerant quantum computer. [Preview Abstract] 
Monday, March 18, 2013 3:42PM  3:54PM 
C27.00007: Virtual Parallel Computing and a Search Algorithm Using Matrix Product States Eduardo Mucciolo, Claudio Chamon We propose a form of parallel computing on classical computers that is based on matrix product states. The virtual parallelization is accomplished by representing bits with matrices and by evolving these matrices from an initial product state that encodes multiple inputs. Matrix evolution follows from the sequential application of gates, as in a logical circuit. The action by classical probabilistic onebit and deterministic twobit gates such as NAND are implemented in terms of matrix operations and, as opposed to quantum computing, it is possible to copy bits. We present a way to explore this method of computation to solve search problems and count the number of solutions. We argue that if the classical computational cost of testing solutions (witnesses) requires less than $O(n^2)$ local twobit gates acting on $n$ bits, the search problem can be fully solved in subexponential time. Therefore, for this restricted type of search problem, the virtual parallelization scheme is faster than Grover's quantum algorithm. [Preview Abstract] 
Monday, March 18, 2013 3:54PM  4:06PM 
C27.00008: Google in a Quantum Network Giuseppe Davide Paparo In [1] we introduce the characterization of a class of quantum PageRank algorithms in a scenario in which some kind of quantum network is realizable out of the current classical internet web, but no quantum computer is yet available. This class of algorithms represents a quantization of the PageRank protocol currently employed to list web pages according to their importance. The PageRank algorithm's ranking ability has been instrumental to give structure to the web. This class of algorithms may be able to rank nodes in a quantum network. Furthermore, in this class, we have found an instance of this class of quantum protocols that outperforms its classical counterpart and may break the classical hierarchy of web pages depending on the topology of the web. \\[4pt] [1] G.D. Paparo and M. A. MartinDelgado; ``Google in a Quantum Network''; Sci.Rep. {\bf 2} , 444 (2012), arXiv:1112.2079. [Preview Abstract] 
Monday, March 18, 2013 4:06PM  4:18PM 
C27.00009: Discretetime quantum walk with history dependence Zlatko Dimcovic, Yevgeniy Kovchegov We study a discrete time quantum walk (DTQW) with explicit correlation (or, memory/history dependence) over previous steps, implemented by a unique evolution operator. Monitoring the paths affects their interferences and we expect appearance of anomalies and classical features, while the process stays unitary. For 2stepmemory we obtain a closedform generating function, with amplitude asymptotic. The trademark ballistic peaks of DTQW remain but a sharp central peak over a few sites appears. For deeper correlations we have so far obtained a full numerical solution for up to 20 memorysteps, evolved over $10,000$'s of timesteps. As memory increases, the amplitude first develops noisy peaks in the middle, and by around 10 stepdeep memory the dominant central peak settles, while the runaway peaks typical of DTQW are all but gone. This central distribution is unlike the Gaussian curve of classical walks, the spreading is still ballistic (albeit slow), the shape stabilizes, and we observe universality. These (and some other) properties appear stable. This behavior starkly differs from previous known results. We use a multidimensional coin, but the precise operator form, explicitly encoding memory dependence in the evolution, comes from our (coinless) interchange framework. [Preview Abstract] 
Monday, March 18, 2013 4:18PM  4:30PM 
C27.00010: Renormalization Group for Quantum Walks Stefan Falkner, Stefan Boettcher, Renato Portugal A renormalization group (RG) treatment of quantum walks holds significant promise for insights into quantum transport phenomena and search algorithms for quantum computing. The generality of this approach has a good chance to elucidate salient characteristics of quantum walks on higherdimensional lattices which at this point are unobtainable with other methods and are even difficult to study numerically. Key questions concern the scaling properties of (unitary) quantum evolution depending on the lattice type. Is there a single exponent describing the meansquare displacement of quantum walks, similar to the scenario observed in ordinary random walks, or is there a spectrum of modes, each with their own exponent? Does quantum interference ensure that these exponents are always smaller than for the respective classical random walks? To what extend do translational invariance and other lattice properties matter? Generally, what is the nature of universality in quantum walks? Our preliminary results on effectively onedimensional lattices demonstrates how RG can be used to study quantum random walks and their asymptotic behavior. [Preview Abstract] 
Monday, March 18, 2013 4:30PM  4:42PM 
C27.00011: Using the graph isomorphism problem to probe differences between discrete and continuoustime quantum random walks Kenneth Rudinger, John King Gamble, Eric Bach, Mark Friesen, Robert Joynt, S. N. Coppersmith Though continuoustime and discretetime quantum walks appear superficially similar, recent studies have demonstrated potential differences in terms of algorithmic power. We investigate these disparities in the context of the graph isomorphism problem. It has been previously demonstrated that discretetime walks of two noninteracting particles can distinguish certain difficulttodistinguish graphs, while it has been proven that continuoustime walks of two noninteracting particles can never distinguish these graphs. We show the origins of this difference in distinguishing power, and find that, even for identical walks, subtle differences in the certificate construction algorithm can nontrivially impact the walk's distinguishing power. [Preview Abstract] 
Monday, March 18, 2013 4:42PM  4:54PM 
C27.00012: Experimental 1D quantum simulation using an oxide nanoelectronics platform Megan Kirkendall, Dongyue Yang, Patrick Irvin, Jeremy Levy, Sangwoo Ryu, ChangBeom Eom We are interested in developing a solid state quantum simulation platform which could be used to study important Hamiltonians like the Hubbard model and investigate phenomena such as high temperature superconductivity. Using the nanoscale control that has been demonstrated in modifying the 2DEG at the LaAlO$_3$/SrTiO$_3$ interface\footnote{Cen, C. \textit{et al}. \textit{Nature Mater}. \textbf{7}, 298302 (2008).}, we are attempting to create an artificial system with which to study these phenomena that is decoupled from the underlying lattice. We use conductive AFM lithography to create onedimensional structures at the LaAlO$_3$/SrTiO$_3$ interface with the goal of determining the relationship between external parameters that can be controlled in the LaAlO$_3$/SrTiO$_3$ system (i.e., $V(x, y)$, back gates, and side gates) and parameters in a Hubbard model description of the physical system. These tools could be used to create a solid state quantum simulation platform providing Hamiltonian level control over artificially created systems. [Preview Abstract] 

C27.00013: ABSTRACT WITHDRAWN 
Monday, March 18, 2013 5:06PM  5:18PM 
C27.00014: Experimental Boson Sampling Andrew White, Matthew Broome, Alessandro Fedrizzi, Saleh RahimiKeshari, Timothy Ralph, Justin Dove, Scott Aaronson Quantum computers are unnecessary for exponentiallyefficient computation or simulation if the Extended ChurchTuring thesisa foundational tenet of computer scienceis correct. The thesis would be directly contradicted by a physical device that efficiently performs a task believed to be intractable for classical computers. Such a task is \textsc{BosonSampling}: obtaining a distribution of $n$ bosons scattered by some linearoptical unitary process. Here we test the central premise of \textsc{BosonSampling}, experimentally verifying that the amplitudes of 3photon scattering processes are given by the permanents of submatrices generated from a unitary describing a 6mode integrated optical circuit. We find the protocol to be robust, working even with the unavoidable effects of photon loss, nonideal sources, and imperfect detection. Strong evidence against the ExtendedChurchTuring thesis will come from scaling to large numbers of photons, which is a much simpler task than building a universal quantum computer. [Preview Abstract] 
Monday, March 18, 2013 5:18PM  5:30PM 
C27.00015: Opening up the Quantum ThreeBox Problem with Undetectable Measurements Richard George, Lucio Robledo, Owen Maroney, Machiel Blok, Hannes Bernien, Daniel Twitchen, Matthew Markham, John Morton, Andrew Briggs, Ronald Hanson One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained as the backaction required by quantum mechanics adding quantum noise to a classical signal. Here we implement the `threebox' quantum game (Aharonov, et al. 1991) by utilising stateoftheart control and measurement of the nitrogen vacancy centre in diamond. In this protocol, the backaction of quantum measurements add no detectable disturbance to the classical description of the game. Quantum and classical mechanics then make contradictory predictions for the same experimental procedure, however classical observers are unable to invoke measurementinduced disturbance to explain the discrepancy. We quantify the disturbance of our measurements and obtain data ruling out any classical model by 7.8 sigma, excluding statedefiniteness from our system. Our experiment is then equivalent to a KochenSpekker test of quantum noncontextuality that successfully addresses the measurement detectability loophole. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2019 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700