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arXiv:quant-ph/0601120 · Physical Review Letters

Globally Controlled Quantum Wires for Perfect Qubit Transport, Mirroring, and Computing

Joseph F. Fitzsimons, Jason Twamley

Published Sep 1, 2006• 121 citations
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Abstract

We describe a new design for a q wire with perfect transmission using a uniformly coupled Ising spin chain subject to global pulses. In addition to allowing for the perfect transport of single qubits, the design also yields the perfect "mirroring" of multiply encoded qubits within the wire. We further utilize this global-pulse generated perfect mirror operation as a "clock cycle" to perform universal quantum computation on these multiply encoded qubits where the interior of the q wire serves as the quantum memory while the q-wire ends perform one- and two-qubit gates.

DOI
10.1103/physrevlett.97.090502

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We describe a new design for a q wire with perfect transmission using a uniformly coupled Ising spin chain subject to global pulses. In addition to allowing for the perfect transport of single qubits, the design also yields the perfect "mirroring" of multiply encoded qubits within the wire. We further utilize this global-pulse generated perfect mirror operation as a "clock cycle" to perform universal quantum computation on these multiply encoded qubits where the interior of the q wire serves as the quantum memory while the q-wire ends perform one- and two-qubit gates.
We present a scheme to perform universal quantum computation using global control with an arbitrary subsystem dimension (not necessarily finite). The scheme is developed over a one spatial dimension NNN-element array, using only mirror-symmetric logical encoding, global pulses for single subsystem operations, uniform Ising-type interaction, and an all zero initial pure state. A mechanism using ancillary degrees of freedom for subsystem specific measurement is also presented.
Quantum processors that combine the long decoherence times of spin qubits together with fast optical manipulation of excitons have recently been the subject of several proposals. Here, I show that arbitrary single- and entangling two-qubit gates can be performed in a chain of perpetually coupled spin qubits solely by using laser pulses to excite higher lying states. It is also demonstrated that universal QC is possible even if these pulses are applied globally to a chain; by employing a repeating pattern of four distinct qubit units, the need for individual qubit addressing is removed. Some current experimental qubit systems would lend themselves to implementing this idea.
Abstract. Quantum processors that combine the long decoherence times of spin qubits together with fast optical manipulation of excitons have recently been the subject of several proposals. I show here that arbitrary single- and entangling twoqubit gates can be performed in a chain of perpetually coupled spin qubits solely by using laser pulses to excite higher lying states. It is also demonstrated that universal quantum computing is possible even if these pulses are applied globally to a chain; by employing a repeating pattern of four distinct qubit units the need for individual qubit addressing is removed. Some current experimental qubit systems would lend themselves to implementing this idea. PACS numbers: 03.67.-a, 03.67.Lx, 78.67.HcGlobal Optical Control of a Quantum Spin Chain 2 1.
We propose a platform to implement a scalable universal quantum computer based on a 2D array of superconducting qubits. Notably, calculations in our scheme are enabled by a set of only three global driving signals, irrespective of the number of qubits, ensuring full scalability of the computation. In stark contrast with the existing literature, global control in our scheme is achieved by leveraging the longitudinal ZZ coupling between neighboring qubits. We show how this enables information flow, one-and two-qubit gates through a series of three global pulses that act together on different subsets of the physical qubits in our system. These findings provide an alternative route to the realization of scalable and fault-tolerant superconducting quantum computers with reduced wiring, bringing them one step closer to solving practical problems in our daily lives.
Heisenberg spin chains can act as quantum wires transferring quantum states either perfectly or with high fidelity. Gaussian packets of excitations passing through dual rails can encode the two states of a logical qubit, depending on which rail is empty and which rail is carrying the packet. With extra interactions in one or between different chains, one can introduce interaction zones in arrays of such chains, where specific one- or two-qubit gates act on any qubit which passes through these interaction zones. Therefore, universal quantum computation is made possible in a static way where no external control is needed. This scheme will then pave the way for a scalable way of quantum computation where specific hardware can be connected to make large quantum circuits. Our scheme is an improvement of a recent scheme where we borrowed an idea from quantum electrodynamics to replace nonlocal interactions between spin chains with local interactions mediated by an ancillary chain.