arXiv subjects

D. Maslov

Publications and source records attributed to D. Maslov.

12 recordsLinked to original sources

arXiv2018

Parallel Entangling Operations on a Universal Ion Trap Quantum Computer

The circuit model of a quantum computer consists of sequences of gate operations between quantum bits (qubits), drawn from a universal family of discrete operations. The ability to execute parallel entangling quantum gates offers clear efficiency gains in numerous quantum circuits as well as for entire algorithms such as Shor's factoring algorithm and quantum simulations. In cases such as full adders and multiple-control Toffoli gates, parallelism can provide an exponential improvement in overall execution time. More importantly, quantum gate parallelism is essential for the practical fault-tolerant error correction of qubits that suffer from idle errors. The implementation of parallel quantum gates is complicated by potential crosstalk, especially between qubits fully connected by a common-mode bus, such as in Coulomb-coupled trapped atomic ions or cavity-coupled superconducting transmons. Here, we present the first experimental results for parallel 2-qubit entangling gates in an array of fully-connected trapped ion qubits. We demonstrate an application of this capability by performing a 1-bit full addition operation on a quantum computer using a depth-4 quantum circuit. These results exploit the power of highly connected qubit systems through classical control techniques, and provide an advance toward speeding up quantum circuits and achieving fault tolerance with trapped ion quantum computers.

quant-ph↗

arXiv2017

Complete 3-Qubit Grover Search on a Programmable Quantum Computer

Searching large databases is an important problem with broad applications. The Grover search algorithm provides a powerful method for quantum computers to perform searches with a quadratic speedup in the number of required database queries over classical computers. It is an optimal search algorithm for a quantum computer, and has further applications as a subroutine for other quantum algorithms. Searches with two qubits have been demonstrated on a variety of platforms and proposed for others, but larger search spaces have only been demonstrated on a non-scalable NMR system. Here, we report results for a complete three-qubit Grover search algorithm using the scalable quantum computing technology of trapped atomic ions, with better-than-classical performance. The algorithm is performed for all 8 possible single-result oracles and all 28 possible two-result oracles. Two methods of state marking are used for the oracles: a phase-flip method employed by other experimental demonstrations, and a Boolean method requiring an ancilla qubit that is directly equivalent to the state-marking scheme required to perform a classical search. All quantum solutions are shown to outperform their classical counterparts. We also report the first implementation of a Toffoli-4 gate, which is used along with Toffoli-3 gates to construct the algorithms; these gates have process fidelities of 70.5% and 89.6%, respectively.

quant-ph↗

arXiv2017

Experimental Comparison of Two Quantum Computing Architectures

We run a selection of algorithms on two state-of-the-art 5-qubit quantum computers that are based on different technology platforms. One is a publicly accessible superconducting transmon device with limited connectivity, and the other is a fully connected trapped-ion system. Even though the two systems have different native quantum interactions, both can be programmed in a way that is blind to the underlying hardware, thus allowing the first comparison of identical quantum algorithms between different physical systems. We show that quantum algorithms and circuits that employ more connectivity clearly benefit from a better connected system of qubits. While the quantum systems here are not yet large enough to eclipse classical computers, this experiment exposes critical factors of scaling quantum computers, such as qubit connectivity and gate expressivity. In addition, the results suggest that co-designing particular quantum applications with the hardware itself will be paramount in successfully using quantum computers in the future.

quant-ph↗

arXiv2010

Transport and elastic scattering times as probes of the nature of impurity scattering in single and bilayer graphene

Both transport $τ_{tr}$ and elastic scattering times $τ_{e}$ are experimentally determined from the carrier density dependence of the magnetoconductance of monolayer and bilayer graphene. Both times and their dependences in carrier density are found to be very different in the monolayer and the bilayer. However their ratio $τ_{tr}/τ_{e} $is found to be of the order of $1.5 $ in both systems and independent of the carrier density. These measurements give insight on the nature (neutral or charged) and spatial extent of the scattering centers. Comparison with theoretical predictions yields that the main scattering mechanism in our graphene samples could be due to strong scatterers of short range, inducing resonant scattering, a likely candidate being vacancies.

cond-mat.mes-hall↗

arXiv2009

Supermetallic conductivity in bromine-intercalated graphite

Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to in-plane charge conductivities which increase monotonically with intercalation time toward values (for ~6 at% Br) that are significantly higher than Cu at temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic susceptibility measurements confirm that the Br dopes the graphene sheets with holes while simultaneously increasing the interplanar separation. The increase of mobility (~ 5E4 cm^2/Vs at T=300 K) and resistance anisotropy together with the reduced diamagnetic susceptibility of the intercalated samples suggests that the observed supermetallic conductivity derives from a parallel combination of weakly-coupled hole-doped graphene sheets.

cond-mat.mtrl-sci↗

arXiv2009

Approximating Fractional Time Quantum Evolution

An algorithm is presented for approximating arbitrary powers of a black box unitary operation, $\mathcal{U}^t$, where $t$ is a real number, and $\mathcal{U}$ is a black box implementing an unknown unitary. The complexity of this algorithm is calculated in terms of the number of calls to the black box, the errors in the approximation, and a certain `gap' parameter. For general $\mathcal{U}$ and large $t$, one should apply $\mathcal{U}$ a total of $\lfloor t \rfloor$ times followed by our procedure for approximating the fractional power $\mathcal{U}^{t-\lfloor t \rfloor}$. An example is also given where for large integers $t$ this method is more efficient than direct application of $t$ copies of $\mathcal{U}$. Further applications and related algorithms are also discussed.

quant-ph↗

arXiv2008

Quantum Circuit Placement

We study the problem of the practical realization of an abstract quantum circuit when executed on quantum hardware. By practical, we mean adapting the circuit to particulars of the physical environment which restricts/complicates the establishment of certain direct interactions between qubits. This is a quantum version of the classical circuit placement problem. We study the theoretical aspects of the problem and also present empirical results that match the best known solutions that have been developed by experimentalists. Finally, we discuss the efficiency of the approach and scalability of its implementation with regards to the future development of quantum hardware.

quant-ph↗

arXiv2008

Quantum Circuit Simplification and Level Compaction

Quantum circuits are time dependent diagrams describing the process of quantum computation. Usually, a quantum algorithm must be mapped into a quantum circuit. Optimal synthesis of quantum circuits is intractable and heuristic methods must be employed. With the use of heuristics, the optimality of circuits is no longer guaranteed. In this paper, we consider a local optimization technique based on templates to simplify and reduce the depth of non-optimal quantum circuits. We present and analyze templates in the general case, and provide particular details for the circuits composed of NOT, CNOT and controlled-sqrt-of-NOT gates. We apply templates to optimize various common circuits implementing multiple control Toffoli gates and quantum Boolean arithmetic circuits. We also show how templates can be used to compact the number of levels of a quantum circuit. The runtime of our implementation is small while the reduction in number of quantum gates and number of levels is significant.

quant-ph↗

arXiv2007

Linear Depth Stabilizer and Quantum Fourier Transformation Circuits with no Auxiliary Qubits in Finite Neighbor Quantum Architectures

In this paper, we investigate how quantum architectures affect the efficiency of the execution of the quantum Fourier transform (QFT) and linear transformations, which are essential parts of the stabilizer/Clifford group circuits. In particular, we show that in most common and realistic physical architectures including the linear nearest neighbor, two-dimensional lattice, and bounded degree graph (containing a chain of length n), n-qubit QFT and n-qubit stabilizer circuits can be parallelized to linear depth using no auxiliary qubits. We construct lower bounds that show the efficiency of our approach.

quant-ph↗

arXiv2007

Quantum information processing using nuclear and electron magnetic resonance: review and prospects

This paper describes recent progress using nuclear magnetic resonance (NMR) as a platform for implementing quantum information processing (QIP) tasks. The basic ideas of NMR QIP are detailed, examining the successes and limitations of liquid and solid state experiments. Finally, a future direction for implementing quantum processors is suggested,utilizing both nuclear and electron spin degrees of freedom.

quant-ph↗

arXiv2006

Techniques for the Synthesis of Reversible Toffoli Networks

This paper presents novel techniques for the synthesis of reversible networks of Toffoli gates, as well as improvements to previous methods. Gate count and technology oriented cost metrics are used. Our synthesis techniques are independent of the cost metrics. Two new iterative synthesis procedure employing Reed-Muller spectra are introduced and shown to complement earlier synthesis approaches. The template simplification suggested in earlier work is enhanced through introduction of a faster and more efficient template application algorithm, updated (shorter) classification of the templates, and presentation of the new templates of sizes 7 and 9. A novel ``resynthesis'' approach is introduced wherein a sequence of gates is chosen from a network, and the reversible specification it realizes is resynthesized as an independent problem in hopes of reducing the network cost. Empirical results are presented to show that the methods are effective both in terms of the realization of all 3x3 reversible functions and larger reversible benchmark specifications.

quant-ph↗

arXiv2000

Unambiguous determination of the g-factor for holes in bismuth at high B/T

Magnetotransport has been investigated in high purity bismuth crystals in static magnetic fields as high as 20 T and temperatures as low as 25 mK. This high B/T ratio permits observation of pronounced Shubnikov-de Haas oscillations over a wide field range and up to fields where most of the carriers are in the lowest Landau level. For transport currents in the bisectrix or binary directions and field in the perpendicular trigonal direction, we have observed doublet splittings centered on each Shubnikov-de Haas oscillation. These splittings exhibit a quadratic dependence on field and disappear before the last oscillation. Our observations allow us to conclude unambiguously that already when the Landau level index is as high as 2 the carriers are fully polarized and that the g-factor for holes with the field in the trigonal direction is 35.3(4).

cond-mat↗