Comment on: "Measuring a Photonic Qubit without Destroying It"

Recently, Pryde et al reported the demonstration of a quantum non-demolition scheme for single-photon polarization states with linear optics and projective measurements [Phys. Rev. Lett. 92, 190402 (2004)]. Here, we argue that their interpretation of the experiment is inconsistent with the fidelity measure they use.Comment: one page, no figure

Entanglement and its Role in Shor's Algorithm

Entanglement has been termed a critical resource for quantum information processing and is thought to be the reason that certain quantum algorithms, such as Shor's factoring algorithm, can achieve exponentially better performance than their classical counterparts. The nature of this resource is still not fully understood: here we use numerical simulation to investigate how entanglement between register qubits varies as Shor's algorithm is run on a quantum computer. The shifting patterns in the entanglement are found to relate to the choice of basis for the quantum Fourier transform.Comment: 15 pages, 4 eps figures, v1-3 were for conference proceedings (not included in the end); v4 is improved following referee comments, expanded explanations and added reference

Power dependence of electric dipole spin resonance

We develop a formalism of electric dipole spin resonance (EDSR) based on slanting magnetic field, where we especially investigate the microwave amplitude dependence. With increasing microwave amplitude, the Rabi frequency increases linearly for a spin confined in a harmonic potential. How- ever, when the spin is confined in the double-well potential, the Rabi frequency shows sub-linear dependence with increasing the microwave amplitude.Comment: 4 pages, conference paper of APPC1

Environmental engineering for quantum energy transport

Transport phenomena are ubiquitous throughout the science, engineering and technology disciplines as it concerns energy, mass, charge and information exchange between systems. In particular, energy transport in the nanoscale regime has attracted significant attention within the physical science community due to its potential to explain complex phenomena like the electronic energy transfer in molecular crystals or the Fenna-Matthews-Olson / light harvesting complexes in photosynthetic bacteria with long time coherences. Energy transport in these systems is highly affected by environmental noise but surprisingly not always in a detrimental way. It was recently found that situations exist where noise actually enhances the transport phenomena. Such noise can take many forms, but can be characterised in three basic behaviours: quantum, coloured or nonlocal. All have been shown potential to offer an energy transport enhancement. The focus of this work is on quantum transport caused by stochastic environment with spatio-temporal correlation. We consider a multi-site nearest neighbour interaction model with pure dephasing environmental noise with coloured and nonlocal character and show how an accelerated rate for the energy transfer results especially under anti-correlation. Negative spatial correlations provide another control parameter to help one establish the most efficient transfer of energy and may provide new insights into the working of exciton transport in photosynthetic complexes. Further the usage of spatio-temporal correlated noise may be a beneficial resource for efficient transport in large scale quantum networks.Comment: 11 pages 5 figure

Blind Justice: What does that mean?

First paragraph: DURING the early Renaissance a number of engravings produced outside of Italy (Dürer (1498) and Bruegel (1561-62)) represented allegories of Justice that offered a very different reading from the later and more familiar Enlightenment interpretations of Justice. What was distinctive about these engravings was the appearance of Justice wearing a blindfold. However, instead of symbolising the impartiality of Justice, as the blindfold commonly does from the C17 onwards, these engravings represent Justice as being blind to its own origins in legal deception and arbitrary violence. Not only in these engravings is Justice made blind to its obscene and violent origins but, it may be interpreted, that these negative attributes are also hidden from us. We are in a sense blind to them