Advances in quantum devices have brought scalable quantum computation closer to reality. We focus on the system-level issues of how quantum devices can be brought together to form a scalable architecture. In particular, we examine promising silicon-based proposals. We discover that communication of quantum data is a critical resource in such proposals. We find that traditional techniques using quantum SWAP gates are exponentially expensive as distances increase and propose quantum teleportation as a means to communicate data over longer distances on a chip. Furthermore, we find that realistic quantum error-correction circuits use a recursive structure that benefits from using teleportation for long-distance communication. We identify a set of important architectural building blocks necessary for constructing scalable communication and computation. Finally, we explore an actual layout scheme for recursive error correction, and demonstrate the exponential growth in communication costs with levels of recursion, and that teleportation limits those costs. Index Terms-Quantum architecture, quantum computers, silicon-based quantum computing. I. INTRODUCTION M ANY important problems seem to require exponential resources on a classical computer. Quantum computers can solve some of these problems with polynomial resources, which has led a great number of researchers to explore quantum information processing technologies [1]-[7]. Early-stage quantum computers have involved a small number Manuscript

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We propose a gravimeter based on a matter-wave resonant cavity loaded with a Bose-Einstein condensate and closed with a sequence of periodic Raman pulses. The gravimeter sensitivity increases quickly with the number of cycles experienced by the condensate inside the cavity. The matter wave is refocused thanks to a spherical wave-front of the Raman pulses. This provides a transverse confinement of the condensate which is discussed in terms of a stability analysis. We develop the analogy of this device with a resonator in momentum space for matter waves.Comment: 15 pages, 6 Figures. The expression for the atomic mirror focal length has been corrected. Other minor corrections and actualizations to the previously published versio

We present an open quantum system theory of atom interferometers evolving in the quantized electromagnetic field bounded by an ideal conductor. Our treatment reveals an unprecedented feature of matter-wave propagation, namely the appearance of a non-local double-path phase coherence. In the standard interpretation of interferometers, one associates well-defined separate phases to individual paths. Our non-local phase coherence is instead associated to pairs of paths. It arises from the coarse-graining over the quantized electromagnetic field and internal atomic degrees of freedom, which play the role of a common reservoir for the pair of paths and lead to a non-Hamiltonian evolution of the atomic waves. We develop a diagrammatic interpretation and estimate the non-local phase for realistic experimental parameters.PACS numbers: 03.75.Dg Atom interferometry [1] has become a field of great importance for both basic and applied science, enabling, in particular, the realization of extremely accurate inertial sensors [2,3]. With the advent of the coherent atomic waves guided on chips [4], the investigation of atom-surface interactions has become a frontier for such systems. Already, atom interferometers have been used to probe the van der Waals regime [5]. This experimental effort calls for a complete theory of atom interferometers in the presence of quantum fluctuations of the electromagnetic (EM) field.In this letter, we layout such theory for a beam of neutral atoms and find an unusual new concept in interferometry: a non-local phase associated to pairs of paths rather than to individual ones. First, we present a theory of atomic phase-shifts taking the effect of field and atomic dipole fluctuations separately over each interferometer arm. This method already contains novel dynamical corrections, which cannot be obtained by standard techniques suitable for atoms driven by conservative forces. However, it neglects quantum correlations, mediated by the field, between the atomic wave-packets evolving along the separate arms. In order to capture this effect, we develop a theory of atom interferometers based on the influence functional method [6], which allows us to derive the non-Hamiltonian evolution of the external atomic observables after coarse-graining over the quantized electromagnetic field and internal atomic (dipole) degrees of freedom. A non-local phase shift arises as a consequence of the finite correlation time of dipole fluctuations interacting across a pair of interferometer paths. It is absent in the standard Hamiltonian treatment of matter-wave dynamics with conservative forces, which shows that the effect of quantum vacuum and zero-point dipole fluctuations on atomic waves cannot be understood as an effective potential.The influence functional method also allows one to consider the decoherence effect [7], another important conse-quence of the non-unitary nature of the matter-wave dynamics. However, in this letter we focus on the non-local real phase shifts beyond the expected loss of contrast in the fri...