Reliable entanglement transfer between pure quantum states

The problem of the reliable transfer of entanglement from one pure bipartite quantum state to another using local operations is analyzed. It is shown that in the case of qubits the amount that can be transferred is restricted to the difference between the entanglement of the two states. In the presence of a catalytic state the range of the transferrable amount broadens to a certain degree.Comment: 6 pages, 4 pictures; revised version; to appear in Phys. Rev.

On the efficiency of nonlocal gates generation

We propose and study a method for using non-maximally entangled states to implement probabilistically non-local gates. Unlike distillation-based protocols, this method does not generate a maximally entangled state at intermediate stages of the process. As a consequences, the method becomes more efficient at a certain range of parameters. Gates of the form $\exp[i\xi\sigma_{n_A}\sigma_{n_B}]$ with $\xi\ll1$, can be implemented with nearly unit probability and with vanishingly small entanglement, while for the distillation-based method the gate is produced with a vanishing success probability. We also derive an upper bound to the optimal success probability and show that in the small entanglement limit, the bound is tight.Comment: 6 pages, 3 figure

The end of Sleeping Beauty's nightmare

The way a rational agent changes her belief in certain propositions/hypotheses in the light of new evidence lies at the heart of Bayesian inference. The basic natural assumption, as summarized in van Fraassen's Reflection Principle ([1984]), would be that in the absence of new evidence the belief should not change. Yet, there are examples that are claimed to violate this assumption. The apparent paradox presented by such examples, if not settled, would demonstrate the inconsistency and/or incompleteness of the Bayesian approach and without eliminating this inconsistency, the approach cannot be regarded as scientific. The Sleeping Beauty Problem is just such an example. The existing attempts to solve the problem fall into three categories. The first two share the view that new evidence is absent, but differ about the conclusion of whether Sleeping Beauty should change her belief or not, and why. The third category is characterized by the view that, after all, new evidence (although hidden from the initial view) is involved. My solution is radically different and does not fall in either of these categories. I deflate the paradox by arguing that the two different degrees of belief presented in the Sleeping Beauty Problem are in fact beliefs in two different propositions, i.e. there is no need to explain the (un)change of belief.Comment: 7 pages, MSWord, to appear in The British Journal for the Philosophy of Scienc

Lower bound on the number of Toffoli gates in a classical reversible circuit through quantum information concepts

The question of finding a lower bound on the number of Toffoli gates in a classical reversible circuit is addressed. A method based on quantum information concepts is proposed. The method involves solely concepts from quantum information - there is no need for an actual physical quantum computer. The method is illustrated on the example of classical Shannon data compression.Comment: 4 pages, 2 figures; revised versio

How Quantum Information can improve Social Welfare

It has been shown elsewhere that quantum resources can allow us to achieve a family of equilibria that can have sometimes a better social welfare, while guaranteeing privacy. We use graph games to propose a way to build non-cooperative games from graph states, and we show how to achieve an unlimited improvement with quantum advice compared to classical advice

Remote operations and interactions for systems of arbitrary dimensional Hilbert space: a state-operator approach

We present a systematic simple method for constructing deterministic remote operations on single and multiple systems of arbitrary discrete dimensionality. These operations include remote rotations, remote interactions and measurements. The resources needed for an operation on a two-level system are one ebit and a bidirectional communication of two cbits, and for an n-level system, a pair of entangled n-level particles and two classical ``nits''. In the latter case, there are $n-1$ possible distinct operations per one n-level entangled pair. Similar results apply for generating interaction between a pair of remote systems and for remote measurements. We further consider remote operations on $N$ spatially distributed systems, and show that the number of possible distinct operations increases here exponentially, with the available number of entangled pairs that are initial distributed between the systems. Our results follow from the properties of a hybrid state-operator object (``stator''), which describes quantum correlations between states and operations.Comment: 18 pages, 3 figures, typo correction