## Other Physics Papers

### Quantum Interrogation and the Safer X-ray (February 2001)

#### (Adrian Kent and David Wallace)

#### Online only; cite as arxiv:quant-ph/0102118.

We investigate quantum interrogation techniques which allow imaging information about semi-transparent objects to be obtained with lower absorption rates than standard classical methods. We show that a gain proportional to log N can be obtained when searching for defects in an array of N pixels, if it is known that at most M of the pixels can have transparencies different from a predetermined theoretical value. A logarithmic gain can also be obtained when searching for infrequently occurring large structures in arrays.

### Simple computer model for the quantum Zeno effect (April 2000)

*Physical Review A* 63 (2001), 022019

This paper presents a simple model for repeated measurement of a quantum system: the evolution of a free particle, simulated by discretising the particle's position. This model is easily simulated by computer and provides a useful arena to investigate the effects of measurement upon dynamics, in particular the slowing of evolution due to measurement (the `quantum Zeno effect'). The results of this simulation are discussed for two rather different sorts of measurement process, both of which are (simplified forms of) measurements used in previous simulations of position measurement. A number of interesting results due to measurement are found, and the investigation casts some light on previous disagreements about the presence or absence of the Zeno effect.

### The quantization of gravity - an introduction (April 2000)

#### Online only; cite as arxiv:gr-qc/0004005.

This is an introduction to quantum gravity, aimed at a fairly general audience and concentrating on what have historically been the two main approaches to quantum gravity: the covariant and canonical programs (string theory is not covered). The quantization of gravity is discussed by analogy with the quantization of the electromagnetic field. The conceptual and technical problems of both approaches are discussed, and the paper concludes with a discussion of evidence for quantum gravity from the rest of physics.

The paper assumes some familiarity with non-relativistic quantum mechanics, special relativity, and the Lagrangian and Hamiltonian formulations of classical mechanics; some experience with classical field theory, quantum electrodynamics and the gauge principle in electromagnetism might be helpful but is not required. No knowledge of general relativity or of quantum field theory in general is assumed.

(**Note**: this is a very old paper of mine, and was never intended for (non-electronic) publication. I've left it available since
various people have said it's a moderately helpful introduction to the issue for complete non-specialists. It doesn't really
say anything that wasn't known in the 1980s.)