Architectures for a quantum random access memory

Vittorio Giovannetti, Seth Lloyd, and Lorenzo Maccone
Phys. Rev. A 78, 052310 – Published 5 November 2008

Abstract

A random access memory, or RAM, is a device that, when interrogated, returns the content of a memory location in a memory array. A quantum RAM, or qRAM, allows one to access superpositions of memory sites, which may contain either quantum or classical information. RAMs and qRAMs with n-bit addresses can access 2n memory sites. Any design for a RAM or qRAM then requires O(2n) two-bit logic gates. At first sight this requirement might seem to make large scale quantum versions of such devices impractical, due to the difficulty of constructing and operating coherent devices with large numbers of quantum logic gates. Here we analyze two different RAM architectures (the conventional fanout and the “bucket brigade”) and propose some proof-of-principle implementations, which show that, in principle, only O(n) two-qubit physical interactions need take place during each qRAM call. That is, although a qRAM needs O(2n) quantum logic gates, only O(n) need to be activated during a memory call. The resulting decrease in resources could give rise to the construction of large qRAMs that could operate without the need for extensive quantum error correction.

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  • Received 7 August 2008

DOI:https://doi.org/10.1103/PhysRevA.78.052310

©2008 American Physical Society

Authors & Affiliations

Vittorio Giovannetti1, Seth Lloyd2, and Lorenzo Maccone3

  • 1NEST CNR-INFM & Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy
  • 2MIT, Research Laboratory of Electronics and Department of Mechanical Engineering, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
  • 3QUIT—Quantum Information Theory Group, Dipartimento di Fisica “A. Volta,” Università di Pavia, via A. Bassi 6, I-27100 Pavia, Italy

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Vol. 78, Iss. 5 — November 2008

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