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Vlatko Vedral

Publications and source records attributed to Vlatko Vedral.

297 records · Page 17Linked to original sources
arXiv2001

A note on quantum one-way permutations

We discuss the question of the existence of quantum one-way permutations. First, we prove the equivalence between inverting a permutation and that of constructing a polynomial size network for reflecting about a given quantum state. Next, we consider the question: if a state is difficult to prepare, is the operator reflecting about that state difficult to construct? By revisiting Grover's algorithm, we present the relationship between this question and the existence of one-way permutations. Moreover, we compare our method to Grover's algorithm and discuss possible applications of our results.

quant-ph↗
arXiv2000

Detection of Geometric Phases in Superconducting Nanocircuits

When a quantum mechanical system undergoes an adiabatic cyclic evolution it acquires a geometrical phase factor in addition to the dynamical one. This effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnologies should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be realized, and show how the effect may applied to the design of gates for quantum computation.

cond-mat.mes-hall↗
arXiv2000

Remote information concentration using a bound entangled state

Remote information concentration, the reverse process of quantum telecloning, is presented. In this scheme, quantum information originally from a single qubit, but now distributed into three spatially separated qubits, is remotely concentrated back to a single qubit via an initially shared entangled state without performing any global operations. This entangled state is an unlockable bound entangled state and we analyze its properties.

quant-ph↗
arXiv2000

Local Distinguishability of Multipartite Orthogonal Quantum States

We consider one copy of a quantum system prepared in one of two orthogonal pure states, entangled or otherwise, and distributed between any number of parties. We demonstrate that it is possible to identify which of these two states the system is in by means of local operations and classical communication alone. The protocol we outline is both completely reliable and completely general - it will correctly distinguish any two orthogonal states 100% of the time.

quant-ph↗
arXiv2000

Geometric phases for mixed states in interferometry

We provide a physical prescription based on interferometry for introducing the total phase of a mixed state undergoing unitary evolution, which has been an elusive concept in the past. We define the parallel transport condition that provides a connection-form for obtaining the geometric phase for mixed states. The expression for the geometric phase for mixed state reduces to well known formulas in the pure state case when a system undergoes noncyclic and unitary quantum evolution.

quant-ph↗
arXiv1999

Quantum information distribution via entanglement

We present a generalization of quantum teleportation that distributes quantum information from a sender's $d$-level particle to $N_o$ particles held by remote receivers via an initially shared multiparticle entangled state. This entangled state functions as a multiparty quantum information distribution channel between the sender and the receivers. The structure of the distribution channel determines how quantum information is processed. Our generalized teleportation scheme allows multiple receivers at arbitrary locations, and can be used for applications such as optimal quantum information broadcasting, asymmetric telecloning, and quantum error correction.

quant-ph↗
arXiv1998

Entanglement in Quantum Information Theory

Quantum mechanics has many counter-intuitive consequences which contradict our intuition which is based on classical physics. Here we discuss a special aspect of quantum mechanics, namely the possibility of entanglement between two or more particles. We will establish the basic properties of entanglement using quantum state teleportation. These principles will then allow us to formulate quantitative measures of entanglement. Finally we will show that the same general principles can also be used to prove seemingly difficult questions regarding entanglement dynamics very easily. This will be used to motivate the hope that we can construct a thermodynamics of entanglement.

quant-ph↗
arXiv1998

Basics of Quantum Computation

Quantum computers require quantum logic, something fundamentally different to classical Boolean logic. This difference leads to a greater efficiency of quantum computation over its classical counter-part. In this review we explain the basic principles of quantum computation, including the construction of basic gates, and networks. We illustrate the power of quantum algorithms using the simple problem of Deutsch, and explain, again in very simple terms, the well known algorithm of Shor for factorisation of large numbers into primes. We then describe physical implementations of quantum computers, focusing on one in particular, the linear ion-trap realization. We explain that the main obstacle to building an actual quantum computer is the problem of decoherence, which we show may be circumvented using the methods of quantum error correction.

quant-ph↗