BioPHYSICAL chemistry

Superconductors play a critical role in many instruments, including mag-
nets used for NMR experiments (Chapter 14). In a SQUID, the electrons
circulate in either a clockwise or counterclockwise motion without any
resistance that would alter the motion. The experiment showed that the
electrons could be considered to be a superposition of the states involv-
ing rotation in either direction. Although this system is not quite as large
as a cat, it does show that billions of electrons collectively can behave
with a strictly quantum-mechanical property. In another experiment
(Gisin 2006; Ourjoumtsev et al. 2006), a light pulse, representing the
cat, is generated as a superposition of two coherent states (Figure 9.11).
A single photon, representing a kitten, is removed from the pulse, which
still contains information concerning the pulse (as what is termed a
Wigner function). While these experiments may appear to be fanciful,
they represent the development of quantum states of propagating light
beams. Such beams could be used for quantum computing and commun-
ication, providing greater speeds and new means for encryption of data
(Bennett & DiVincenzo 2000).

CHAPTER 9 QUANTUM THEORY 195

Frequency

doubler

Parametric

Filter amplifier

Laser

Filter

Detector Detector

Detector

1 2

? 3

Figure 9.11Femtosecond laser pulses are generated that induce the formation of photons
corresponding to small Schrödinger kittens. Modified from Gisin (2006).

References

Bennett, C.H. and DiVincenzo, D.P. (2000) Quantum
information and computation. Nature 404 , 247–55.
Blatter, G. (2000) Schrödinger’s cat is now fat.
Nature 406 , 25 – 6.
Friedman, J.R., Patel, V., Chen, W., Tolpygo, S.K.,
and Lukens, J.E. (2000) Quantum superposition
of distinct macroscopic states. Nature 406 , 43 – 6.
Gisin, N. (2006) New additions to the Schrödinger
cat family. Science 312 , 63 – 4.

Ourjoumtsev, A., Tualle-Brouri, R., Lauret, J., and

Grangler, P. (2006) Generating optical Schrödinger

kittens for quantum information processing. Science

312 , 83 – 6.

Schrödinger, E. (1935) Die genenwartige situation

in der quantenmechanik. Naturwissenschaftern 23 ,

807–12; 823 – 8; 844 –9.