Schools of Chemistry and Biochemistry

Schools of Chemistry and Biochemistry

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Monroe C.,University of Maryland University College | Raussendorf R.,University of British Columbia | Ruthven A.,University of British Columbia | Brown K.R.,Schools of Chemistry and Biochemistry | And 4 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

The practical construction of scalable quantum-computer hardware capable of executing nontrivial quantum algorithms will require the juxtaposition of different types of quantum systems. We analyze a modular ion trap quantum-computer architecture with a hierarchy of interactions that can scale to very large numbers of qubits. Local entangling quantum gates between qubit memories within a single register are accomplished using natural interactions between the qubits, and entanglement between separate registers is completed via a probabilistic photonic interface between qubits in different registers, even over large distances. We show that this architecture can be made fault tolerant, and demonstrate its viability for fault-tolerant execution of modest size quantum circuits. © 2014 American Physical Society.

Tomita Y.,Schools of Chemistry and Biochemistry | Merrill J.T.,Schools of Chemistry and Biochemistry | Brown K.R.,Schools of Chemistry and Biochemistry
New Journal of Physics | Year: 2010

The Hamiltonian control of n qubits requires precision control of both the strength and timing of interactions. Compensation pulses relax the precision requirements by reducing unknown but systematic errors. Using composite pulse techniques designed for single qubits, we show that systematic errors for n-qubit systems can be corrected to arbitrary accuracy given either two non-commuting control Hamiltonians with identical systematic errors or one error-free control Hamiltonian. We also examine composite pulses in the context of quantum computers controlled by two-qubit interactions. For quantum computers based on the XY interaction, single-qubit composite pulse sequences naturally correct systematic errors. For quantum computers based on the Heisenberg or exchange interaction, the composite pulse sequences reduce the logical single-qubit gate errors but increase the errors for logical two-qubit gates. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Goeders J.E.,Schools of Chemistry and Biochemistry | Clark C.R.,Schools of Chemistry and Biochemistry | Vittorini G.,Schools of Chemistry and Biochemistry | Wright K.,Schools of Chemistry and Biochemistry | And 2 more authors.
Journal of Physical Chemistry A | Year: 2013

The masses of single molecular ions are nondestructively measured by cotrapping the ion of interest with a laser-cooled atomic ion, 40Ca+. Measurement of the resolved sidebands of a dipole forbidden transition on the atomic ion reveals the normal-mode frequencies of the two ion system. The mass of two molecular ions, 40CaH+ and 40Ca16O+, are then determined from the normal-mode frequencies. Isotopes of Ca+ are used to determine the effects of stray electric fields on the normal mode measurement. The future use of resolved sideband experiments for molecular spectroscopy is also discussed. © 2013 American Chemical Society.

Gutierrez M.,Schools of Chemistry and Biochemistry | Brown K.R.,Schools of Chemistry and Biochemistry
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

Classical simulations of noisy stabilizer circuits are often used to estimate the threshold of a quantum error-correcting code. Physical noise sources are efficiently approximated by random insertions of Pauli operators. For a single qubit, more accurate approximations that still allow for efficient simulation can be obtained by including Clifford operators and Pauli operators conditional on measurement. We examine the feasibility of employing these expanded error approximations to obtain better threshold estimates. We calculate the level-1 pseudothreshold for the Steane [[7,1,3]] code for amplitude damping and dephasing along a non-Clifford axis. The expanded channels estimate the actual channel action more accurately than the Pauli channels before error correction. However, after error correction, the Pauli twirling approximation yields very accurate estimates of the performance of quantum error-correcting protocols in the presence of the actual noise channel. © 2015 American Physical Society.

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