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150
The Computational Complexity of Linear Optics
 in Proceedings of STOC 2011
"... We give new evidence that quantum computers—moreover, rudimentary quantumcomputers built entirely out of linearoptical elements—cannotbeefficientlysimulatedbyclassical computers. In particular, we define a model of computation in which identical photons are generated, sent through a linearoptical n ..."
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Cited by 34 (8 self)
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We give new evidence that quantum computers—moreover, rudimentary quantumcomputers built entirely out of linearoptical elements—cannotbeefficientlysimulatedbyclassical computers. In particular, we define a model of computation in which identical photons are generated, sent through a linearoptical network, then nonadaptively measured to count the number of photons in each mode. This model is not known or believed to be universal for quantum computation, and indeed, we discuss the prospects for realizing the model using current technology. On the other hand, we prove that the model is able to solve sampling problems and search problems that are classically intractable under plausible assumptions. Our first result says that, if there exists a polynomialtime classical algorithm that samples from the same probability distribution as a linearoptical network, then P #P = BPP NP, and hence the polynomial hierarchy collapses to the third level. Unfortunately, this result assumes an extremely accurate simulation. Our main result suggests that even an approximate or noisy classical simulation would already imply a collapse of the polynomial hierarchy. For this, we need two unproven conjectures: the PermanentofGaussians Conjecture, which says that it is #Phard to approximate the permanent of a matrixAofindependentN (0,1)Gaussianentries, withhigh probability over A; and the Permanent AntiConcentration Conjecture, which says that Per(A)  ≥ √ n!/poly(n) with high probability over A. We present evidence for these conjectures, both of which seem interesting even apart from our application. For the 96page full version, see www.scottaaronson.com/papers/optics.pdf
Architectural implications of quantum computing technologies
 ACM Journal on Emerging Technologies in Computing Systems (JETC
, 2006
"... In this article we present a classification scheme for quantum computing technologies that is based on the characteristics most relevant to computer systems architecture. The engineering tradeoffs of execution speed, decoherence of the quantum states, and size of systems are described. Concurrency, ..."
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Cited by 27 (4 self)
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In this article we present a classification scheme for quantum computing technologies that is based on the characteristics most relevant to computer systems architecture. The engineering tradeoffs of execution speed, decoherence of the quantum states, and size of systems are described. Concurrency, storage capacity, and interconnection network topology influence algorithmic efficiency, while quantum error correction and necessary quantum state measurement are the ultimate drivers of logical clock speed. We discuss several proposed technologies. Finally, we use our taxonomy to explore architectural implications for common arithmetic circuits, examine the implementation of quantum error correction, and discuss clusterstate quantum computation.
Quantum Circuit Simplification and Level Compaction
 in IEEE Transactions on ComputerAided Design of Integrated Circuits and Systems, 2008
"... Abstract—Quantum circuits are timedependent diagrams describing the process of quantum computation. Usually, a quantum algorithm must be mapped into a quantum circuit. Optimal synthesis of quantum circuits is intractable, and heuristic methods must be employed. With the use of heuristics, the optim ..."
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Cited by 25 (4 self)
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Abstract—Quantum circuits are timedependent diagrams describing the process of quantum computation. Usually, a quantum algorithm must be mapped into a quantum circuit. Optimal synthesis of quantum circuits is intractable, and heuristic methods must be employed. With the use of heuristics, the optimality of circuits is no longer guaranteed. In this paper, we consider a local optimization technique based on templates to simplify and reduce the depth of nonoptimal quantum circuits. We present and analyze templates in the general case and provide particular details for the circuits composed of NOT, CNOT, and controlledsqrtofNOT gates. We apply templates to optimize various common circuits implementing multiple control Toffoli gates and quantum Boolean arithmetic circuits. We also show how templates can be used to compact the number of levels of a quantum circuit. The runtime of our implementation is small, whereas the reduction in the number of quantum gates and number of levels is significant. Index Terms—Circuit optimization, quantum circuits, time optimization. I.
Circuit for Shor’s algorithm using 2n+3 qubits
 54
, 2002
"... We try to minimize the number of qubits needed to factor an integer of n bits using Shor’s algorithm on a quantum computer. We introduce a circuit which uses 2n+3 qubits and O(n 3 lg(n)) elementary quantum gates in a depth of O(n 3) to implement the factorization algorithm. The circuit is computable ..."
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Cited by 22 (0 self)
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We try to minimize the number of qubits needed to factor an integer of n bits using Shor’s algorithm on a quantum computer. We introduce a circuit which uses 2n+3 qubits and O(n 3 lg(n)) elementary quantum gates in a depth of O(n 3) to implement the factorization algorithm. The circuit is computable in polynomial time on a classical computer and is completely general as it does not rely on any property of the number to be factored. 1
The Effect of Communication Costs in SolidState Quantum Computing Architectures
, 2003
"... Quantum computation has become an intriguing technology with which to attack difficult problems and to enhance system security. Quantum algorithms, however, have been analyzed under idealized assumptions without important physical constraints in mind. In this paper, we analyze two key constraints: t ..."
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Cited by 17 (3 self)
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Quantum computation has become an intriguing technology with which to attack difficult problems and to enhance system security. Quantum algorithms, however, have been analyzed under idealized assumptions without important physical constraints in mind. In this paper, we analyze two key constraints: the short spatial distance of quantum interactions and the short temporal life of quantum data. In particular, quantum computations must make use of extremely robust error correction techniques to extend the life of quantum data. We present optimized spatial layouts of quantum error correction circuits for quantum bits embedded in silicon. We analyze the complexity of error correction under the constraint that interaction between these bits is near neighbor and data must be propagated via swap operations from one part of the circuit to another. We discover two interesting results from our quantum layouts. First, the recursive nature of quantum error correction circuits requires a additional communication technique more powerful than nearneighbor swaps – too much error accumulates if we attempt to swap over long distances. We show that quantum teleportation can be used to implement recursive structures. We also show that the reliability of the quantum swap operation is the limiting factor in solidstate quantum computation.
Quantum computing with trapped ions
, 2008
"... Quantum computers hold the promise to solve certain computational task much more efficiently than classical computers. We review the recent experimental advancements towards a quantum computer with trapped ions. In particular, various implementations of qubits, quantum gates and some key experiments ..."
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Cited by 17 (2 self)
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Quantum computers hold the promise to solve certain computational task much more efficiently than classical computers. We review the recent experimental advancements towards a quantum computer with trapped ions. In particular, various implementations of qubits, quantum gates and some key experiments are discussed. Furthermore, we review some implementations of quantum algorithms such as a deterministic teleportation of quantum information and an error correction scheme.
RevKit: A Toolkit for Reversible Circuit Design
"... Abstract—In recent years, research in the domain of reversible circuit design has attracted significant attention leading to many different approaches for e.g. synthesis, optimization, simulation, verification, and test. However, most of the resulting tools are not publicly available. In this paper, ..."
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Cited by 15 (10 self)
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Abstract—In recent years, research in the domain of reversible circuit design has attracted significant attention leading to many different approaches for e.g. synthesis, optimization, simulation, verification, and test. However, most of the resulting tools are not publicly available. In this paper, we introduce RevKit, an open source toolkit that aims to make recent developments in reversible circuit design accessible to other researchers. Therefore, a modular and extendable framework is provided which easily enables the addition of new methods and tools. RevKit already provides some of the existing approaches for synthesis, optimization, and verification functionality. I. INTRODUCTION AND BACKGROUND The development of computing machines has found great success in the last decades. Nowadays billions of components are built on a few square centimeters – and this increasing
SyReC: A programming language for synthesis of reversible circuits
 in Forum on Specification and Design Languages, 2010
"... Abstract—Reversible logic serves as a basis for emerging technologies like quantum computing and additionally has applications in lowpower design. In particular, since traditional technologies like CMOS are going to reach their limits in the near future, reversible logic has been established as a ..."
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Cited by 14 (10 self)
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Abstract—Reversible logic serves as a basis for emerging technologies like quantum computing and additionally has applications in lowpower design. In particular, since traditional technologies like CMOS are going to reach their limits in the near future, reversible logic has been established as a promising alternative. Thus, in the last years this area started to become intensely studied by researchers. In particular, how to efficiently synthesize complex reversible circuits is an important question. So far, only synthesis approaches are available that rely on Boolean function representations, like e.g. truth tables or decision diagrams. In this paper, we propose the programming language SyReC that allows to specify and afterwards to automatically synthesize reversible circuits. Using an existing programming language for reversible software design as basis, we introduce new concepts, operations, and restrictions allowing the specification of reversible hardware. Furthermore, a hierarchical approach is presented that automatically transforms the respective statements and operations of the new programming language into a reversible circuit. Experiments show that with the proposed method, complex circuits can be easily specified and synthesized while with previous approaches this often is not possible due to the limits caused by truth tables or decision diagrams. I.