12,144 research outputs found

### Programmable networks for quantum algorithms

The implementation of a quantum computer requires the realization of a large
number of N-qubit unitary operations which represent the possible oracles or
which are part of the quantum algorithm. Until now there are no standard ways
to uniformly generate whole classes of N-qubit gates. We have developed a
method to generate arbitrary controlled phase shift operations with a single
network of one-qubit and two-qubit operations. This kind of network can be
adapted to various physical implementations of quantum computing and is
suitable to realize the Deutsch-Jozsa algorithm as well as Grover's search
algorithm.Comment: 4 pages. Accepted version; Journal-ref. adde

### Exact two-qubit universal quantum circuit

We provide an analytic way to implement any arbitrary two-qubit unitary
operation, given an entangling two-qubit gate together with local gates. This
is shown to provide explicit construction of a universal quantum circuit that
exactly simulates arbitrary two-qubit operations in SU(4). Each block in this
circuit is given in a closed form solution. We also provide a uniform upper
bound of the applications of the given entangling gates, and find that exactly
half of all the Controlled-Unitary gates satisfy the same upper bound as the
CNOT gate. These results allow for the efficient implementation of operations
in SU(4) required for both quantum computation and quantum simulation.Comment: 5 page

### Adiabatic Quantum Computation and Deutsch's Algorithm

We show that by a suitable choice of a time dependent Hamiltonian, Deutsch's
algorithm can be implemented by an adiabatic quantum computer. We extend our
analysis to the Deutsch-Jozsa problem and estimate the required running time
for both global and local adiabatic evolutions.Comment: 6 Pages, Revtex. Typos corrected, references added. Published versio

### Spectral geometry of spacetime

Spacetime, understood as a globally hyperbolic manifold, may be characterized
by spectral data using a 3+1 splitting into space and time, a description of
space by spectral triples and by employing causal relationships, as proposed
earlier. Here, it is proposed to use the Hadamard condition of quantum field
theory as a smoothness principle.Comment: AMS-LaTeX, 6 pages,Talk presented at the Euroconference on
"Non-Commutative Geometry And Hopf Algebras In Field Theory And Particle
Physics" Torino, Villa Gualino, September 20 - 30, 199

### Logic programming as quantum measurement

The emphasis is made on the juxtaposition of (quantum~theorem) proving versus
quantum (theorem~proving). The logical contents of verification of the
statements concerning quantum systems is outlined. The Zittereingang (trembling
input) principle is introduced to enhance the resolution of predicate
satisfiability problem provided the processor is in a position to perform
operations with continuous input. A realization of Zittereingang machine by a
quantum system is suggested.Comment: 11 pages, latex, paper accepted for publication in the International
Journal of Theoretical Physic

### Clifford algebras and universal sets of quantum gates

In this paper is shown an application of Clifford algebras to the
construction of computationally universal sets of quantum gates for $n$-qubit
systems. It is based on the well-known application of Lie algebras together
with the especially simple commutation law for Clifford algebras, which states
that all basic elements either commute or anticommute.Comment: 4 pages, REVTeX (2 col.), low-level language corrections, PR

### A conditional quantum phase gate between two 3-state atoms

We propose a scheme for conditional quantum logic between two 3-state atoms
that share a quantum data-bus such as a single mode optical field in cavity QED
systems, or a collective vibrational state of trapped ions. Making use of
quantum interference, our scheme achieves successful conditional phase
evolution without any real transitions of atomic internal states or populating
the quantum data-bus. In addition, it only requires common addressing of the
two atoms by external laser fields.Comment: 8 fig

### Entanglement between an electron and a nuclear spin 1/2

We report on the preparation and detection of entangled states between an
electron spin 1/2 and a nuclear spin 1/2 in a molecular single crystal. These
were created by applying pulses at ESR (9.5 GHz) and NMR (28 MHz) frequencies.
Entanglement was detected by using a special entanglement detector sequence
based on a unitary back transformation including phase rotation.Comment: 4 pages, 3 figure

### Entangled Mixed States and Local Purification

Linden, Massar and Popescu have recently given an optimization argument to
show that a single two-qubit Werner state, or any other mixture of the
maximally entangled Bell states, cannot be purified by local operations and
classical communications. We generalise their result and give a simple
explanation. In particular, we show that no purification scheme using local
operations and classical communications can produce a pure singlet from any
mixed state of two spin-1/2 particles. More generally, no such scheme can
produce a maximally entangled state of any pair of finite-dimensional systems
from a generic mixed state. We also show that the Werner states belong to a
large class of states whose fidelity cannot be increased by such a scheme.Comment: 3 pages, Latex with Revtex. Small clarifications and reference adde

### Simple scheme for implementing the Deutsch-Jozsa algorithm in thermal cavity

We present a simple scheme to implement the Deutsch-Jozsa algorithm based on
two-atom interaction in a thermal cavity. The photon-number-dependent parts in
the evolution operator are canceled with the strong resonant classical field
added. As a result, our scheme is immune to thermal field, and does not require
the cavity to remain in the vacuum state throughout the procedure. Besides,
large detuning between the atoms and the cavity is not necessary neither,
leading to potential speed up of quantum operation. Finally, we show by
numerical simulation that the proposed scheme is equal to demonstrate the
Deutsch-Jozsa algorithm with high fidelity.Comment: 7 pages, 4 figure

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