# Robert Griffiths

Robert Griffiths received his B.A. in Physics from Princeton University, then his M.S. and Ph.D. in Physics from Stanford University. Since joining the Department of Physics of Carnegie Mellon University, he has won several fellowships and awards, including the US Senior Scientist Award of the Alexander von Humboldt Foundation, the Cressy Morrison Award of the New York Academy of Sciences, and the Dannie Heineman Prize for Mathematical Physics. He was also elected to the National Academy of Sciences. He is the originator of the consistent histories approach to quantum mechanics, and a correlation inequality for ferromagnetic spin systems was named after him.

Quantum mechanics is hard to understand not only because it involves unfamiliar mathematics, but also because the usual discussion in textbooks about how to relate the mathematics to the real world is incomplete. Supplying the missing link(s) and working out a fully consistent form of quantum theory is the goal of a research program which I initiated in 1984, and which, with major contributions by Roland Omnes, Murray Gell-Mann, and James Hartle, has resulted in what is now called the consistent (or decoherent) history approach to quantum theory. So far as is known at present, this approach is powerful enough to resolve the various quantum paradoxes (Schrodinger's cat, Einstein-Podolsky-Rosen, etc.) without any mysterious action-at-a-distance, and it makes good sense out of quantum measurements. I have written a book Consistent Quantum Theory (Cambridge University Press) which explains the essentials of this approach.

At present my research program is focused on applying consistent history methods and ideas to quantum information theory and quantum computation. Using the principle that quantum measurements, when properly interpreted, reveal a property of the measured system before the measurement took place, C.-S. Niu and I showed that one could greatly simplify the final step in Shor's algorithm for factoring long numbers. We made similar applications to eavesdropping in quantum cryptography. Understanding the significance of density matrices and entangled quantum states, and investigating the noise produced by quantum copying processes, are among the projects currently underway in my research group. We are also looking for (special) relativistic counterparts of some aspects of the consistent history interpretation which at present are best understood for nonrelativistic systems. For further information about my research group see its web page.

My other interests include the problem of irreversibility in statistical mechanics, and various issues, such as determinism and free will, at the interface between science and Christian theology.

## Students

Title | Position | |
---|---|---|

Dan Stahlke | Postdoctoral Fellow | dan@stahlke.org |

"Ising model for the λ transition and phase separation in He 3-He 4 mixtures," Blume, M., V. J. Emery, and Robert B. Griffiths, Phys. Rev. A. 4, 3 (1971)

"Nonanalytic behavior above the critical point in a random Ising ferromagnet," Griffiths, Robert B., Phys. Rev. Let. 23, no. 1 (1969)

"Critical points in multicomponent systems," Griffiths, Robert B., and John C. Wheeler., Phys. Rev. A. 2, no. 3 (1970)

"Consistent histories and the interpretation of quantum mechanics," Griffiths, Robert B., Journal of Statistical Physics 36, no. 1-2 (1984)

"Optimal eavesdropping in quantum cryptography. I. Information bound and optimal strategy," Fuchs, Christopher A., Nicolas Gisin, Robert B. Griffiths, Chi-Sheng Niu, and Asher Peres, Phys. Rev. A. 56, no. 2 (1997)

Reply to "comment on 'Particle path through a nested Mach-Zehnder interferometer'l, Griffiths, R.B." Physical Review A 97(2),026102 (2018)

"Quantum Information: What is it all about?" Griffiths, R.B. Entropy 19(12), 645 (2017).

"What quantum measurements measure." Griffiths, R.B. Physical Review A 96(3), 032110 (2017).

"Degradable quantum channels using pure-state to product-of-pure-state isometries." Siddhu, V., Griffiths, R.B. Physical Review A 94(5), 052331 (2016).

"Particle path through a nested Mach-Zehnder interferometer." Griffiths, R.B. Physical Review A 94(3), 032115 (2016).