The science of quantum information has arisen over the last two decades centered on manipulation individual quanta information, known as bits or qubits. Quantum computers, cryptography, and teleportation are among most celebrated ideas that have emerged from this new field. It was realized later using continuous-variable carriers, instead qubits, constitutes an extremely powerful alternative approach to processing. This review focuses processes rely any combination Gaussian states,...

Feynman's 1982 conjecture, that quantum computers can be programmed to simulate any local system, is shown correct.

Quantum mechanics, through the Heisenberg uncertainty principle, imposes limits on precision of measurement. Conventional measurement techniques typically fail to reach these limits. bounds measurements such as shot noise limit or standard quantum are not fundamental and can be beaten using strategies that employ "quantum tricks" squeezing entanglement.

Solving linear systems of equations is a common problem that arises both on its own and as subroutine in more complex problems: given matrix $A$ vector $\stackrel{\ensuremath{\rightarrow}}{b}$, find $\stackrel{\ensuremath{\rightarrow}}{x}$ such $A\stackrel{\ensuremath{\rightarrow}}{x}=\stackrel{\ensuremath{\rightarrow}}{b}$. We consider the case where one does not need to know solution itself, but rather an approximation expectation value some operator associated with...

We point out a general framework that encompasses most cases in which quantum effects enable an increase precision when estimating parameter (quantum metrology). The typical enhancement is of the order square root number times system sampled. prove this optimal, and we different strategies (classical quantum) permit one to attain bound.

We propose a novel dynamical method for beating decoherence and dissipation in open quantum systems. demonstrate the possibility of filtering out effects unwanted (not necessarily known) system-environment interactions show that noise-suppression procedure can be combined with capability retaining control over effective evolution system. Implications information processing are discussed.

Supervised machine learning is the classification of new data based on already classified training examples. In this work, we show that support vector machine, an optimized binary classifier, can be implemented a quantum computer, with complexity logarithmic in size vectors and number cases when classical sampling algorithms require polynomial time, exponential speed-up obtained. At core big algorithm non-sparse matrix exponentiation technique for efficiently performing inversion...

The dynamics of a decohering two-level system driven by suitable control Hamiltonian is studied. procedure implemented as sequence radio-frequency pulses that repetitively flip the state system, technique can be termed quantum ``bang-bang'' after its classical analog. Decoherence introduced system's interaction with environment shown to washed out completely in limit continuous flipping and greatly suppressed provided interval between made comparable correlation time environment. model...

A qubit was designed that can be fabricated with conventional electron beam lithography and is suited for integration into a large quantum computer. The consists of micrometer-sized loop three or four Josephson junctions; the two states have persistent currents opposite direction. Quantum superpositions these are obtained by pulsed microwave modulation enclosed magnetic flux in control lines. superconducting transporter allows controlled transfer between qubits generated currents, leading to...

Energy transfer within photosynthetic systems can display quantum effects such as delocalized excitonic transport. Recently, direct evidence of long-lived coherence has been experimentally demonstrated for the dynamics Fenna–Matthews–Olson (FMO) protein complex [Engel et al., Nature (London) 446, 782 (2007)]. However, relevance dynamical processes to exciton efficiency is a large extent unknown. Here, we develop theoretical framework studying role interference in energy molecular arrays...

This paper provides necessary and sufficient conditions for constructing a universal quantum computer over continuous variables. As an example, it is shown how the amplitudes of electromagnetic field might be constructed using simple linear devices such as beam splitters phase shifters, together with squeezers nonlinear Kerr-effect fibers atoms in optical cavities. Such device could principle perform ``quantum floating point'' computations. Problems involving noise, finite precision, error...

Microwave spectroscopy experiments have been performed on two quantum levels of a macroscopic superconducting loop with three Josephson junctions. Level repulsion the ground state and first excited is found where classical persistent-current states opposite polarity are degenerate, indicating symmetric antisymmetric superpositions states. The persistent currents 0.5 microampere correspond to center-of-mass motion millions Cooper pairs.

A random access memory (RAM) uses n bits to randomly address N=2(n) distinct cells. quantum (QRAM) qubits any superposition of N We present an architecture that exponentially reduces the requirements for a call: O(logN) switches need be thrown instead used in conventional (classical or quantum) RAM designs. This yields more robust QRAM algorithm, as it general requires entanglement among less gates, and leads exponential decrease power needed addressing. optical implementation is presented.

The use of quantum-mechanically entangled light to illuminate objects can provide substantial enhancements over unentangled for detecting and imaging those in the presence high levels noise loss. Each signal sent out is with an ancilla, which retained. Detection takes place via entangling measurement on returning together ancilla. This paper shows that photodetection, quantum illumination m bits entanglement principle increase effective signal-to-noise ratio by a factor 2 , exponential...

We present the design of a superconducting qubit that has circulating currents opposite sign as its two states. The circuit consists three nano-scale aluminum Josephson junctions connected in loop and controlled by magnetic fields. advantages this are it can be made insensitive to background charges substrate, flux states detected with SQUID, manipulated Coupled systems qubits also discussed well sources decoherence.

We describe a new polynomial time quantum algorithm that uses the fast Fourier transform to find eigenvalues and eigenvectors of local Hamiltonian, can be applied in cases (commonly found ab initio physics chemistry problems) for which all known classical algorithms require exponential time. Applications specific problems are considered, we classically intractable interesting from atomic may solved with between 50 100 bits.

An upper limit is given to the amount of quantum information that can be transmitted reliably down a noisy, decoherent channel. A class error-correcting codes presented allow attain this limit. The result analog Shannon's bound and code for noisy classical

We provide fast algorithms for simulating many-body Fermi systems on a universal quantum computer. Both first and second quantized descriptions are considered, the relative computational complexities determined in each case. In order to accommodate fermions using Hamiltonian, an efficient algorithm antisymmetrization is given. Finally, simulation of Hubbard model discussed detail.

It is shown that if one can apply some Hamiltonian repeatedly to a few variables at time in general effect any desired unitary evolution on an arbitrarily large number of variables. As result, almost quantum logic gate with two or more inputs computationally universal copies the be ``wired together'' circuit, and perform transformation set

An optical transmitter irradiates a target region containing bright thermal-noise bath in which low-reflectivity object might be embedded. The light received from this is used to decide whether the present or absent. performance achieved using coherent-state compared with that of quantum-illumination transmitter, i.e., one employs signal beam obtained spontaneous parametric down-conversion. By making optimum joint measurement on together retained down-conversion idler beam, system realizes 6...

Arrays of weakly coupled quantum systems might compute if subjected to a sequence electromagnetic pulses well-defined frequency and length. Such pulsed arrays are true computers: Bits can be placed in superpositionsof 0 1, logical operations take place coherently, dissipation is required only for error correction. Operated with frequent correction, such system functions as parallel digital computer. quantum-mechanically coherent manner, device generalpurpose quantum-mechanical...