6,172 research outputs found
Arithmetic on a Distributed-Memory Quantum Multicomputer
We evaluate the performance of quantum arithmetic algorithms run on a
distributed quantum computer (a quantum multicomputer). We vary the node
capacity and I/O capabilities, and the network topology. The tradeoff of
choosing between gates executed remotely, through ``teleported gates'' on
entangled pairs of qubits (telegate), versus exchanging the relevant qubits via
quantum teleportation, then executing the algorithm using local gates
(teledata), is examined. We show that the teledata approach performs better,
and that carry-ripple adders perform well when the teleportation block is
decomposed so that the key quantum operations can be parallelized. A node size
of only a few logical qubits performs adequately provided that the nodes have
two transceiver qubits. A linear network topology performs acceptably for a
broad range of system sizes and performance parameters. We therefore recommend
pursuing small, high-I/O bandwidth nodes and a simple network. Such a machine
will run Shor's algorithm for factoring large numbers efficiently.Comment: 24 pages, 10 figures, ACM transactions format. Extended version of
Int. Symp. on Comp. Architecture (ISCA) paper; v2, correct one circuit error,
numerous small changes for clarity, add reference
Fast Quantum Modular Exponentiation
We present a detailed analysis of the impact on modular exponentiation of
architectural features and possible concurrent gate execution. Various
arithmetic algorithms are evaluated for execution time, potential concurrency,
and space tradeoffs. We find that, to exponentiate an n-bit number, for storage
space 100n (twenty times the minimum 5n), we can execute modular exponentiation
two hundred to seven hundred times faster than optimized versions of the basic
algorithms, depending on architecture, for n=128. Addition on a neighbor-only
architecture is limited to O(n) time when non-neighbor architectures can reach
O(log n), demonstrating that physical characteristics of a computing device
have an important impact on both real-world running time and asymptotic
behavior. Our results will help guide experimental implementations of quantum
algorithms and devices.Comment: to appear in PRA 71(5); RevTeX, 12 pages, 12 figures; v2 revision is
substantial, with new algorithmic variants, much shorter and clearer text,
and revised equation formattin
Efficient one- and two-qubit pulsed gates for an oscillator stabilized Josephson qubit
We present theoretical schemes for performing high-fidelity one- and
two-qubit pulsed gates for a superconducting flux qubit. The "IBM qubit"
consists of three Josephson junctions, three loops, and a superconducting
transmission line. Assuming a fixed inductive qubit-qubit coupling, we show
that the effective qubit-qubit interaction is tunable by changing the applied
fluxes, and can be made negligible, allowing one to perform high fidelity
single qubit gates. Our schemes are tailored to alleviate errors due to 1/f
noise; we find gates with only 1% loss of fidelity due to this source, for
pulse times in the range of 20-30ns for one-qubit gates (Z rotations,
Hadamard), and 60ns for a two-qubit gate (controlled-Z). Our relaxation and
dephasing time estimates indicate a comparable loss of fidelity from this
source. The control of leakage plays an important role in the design of our
shaped pulses, preventing shorter pulse times. However, we have found that
imprecision in the control of the quantum phase plays the major role in the
limitation of the fidelity of our gates.Comment: Published version. Added references. Corrected minor typos. Added
discussion on how the influence of 1/f noise is modeled. 36 pages, 11 figure
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