Asher Peres

Asher Peres, one of the pioneers of quantum information theory, and a notable contributor to many other areas of physics, passed away a few days ago.

Asher was, among many other things, and in no particular order:

• Very kind and encouraging to a certain very young quantum information theorist he met at the Institute for Theoretical Physics in Santa Barbara in 1996.
• Passionate about physics, with a very independent point of view.
• The author of a wonderful textbook on the foundations of quantum mechanics, which I strongly recommend to anyone who’s taken a basic course in quantum physics.

  In 1994 I was doing my undergraduate thesis on Bell’s inequality and possible connections to quasidistribution functions. Excepting Bell’s orignal paper and some papers by Mermin, I was having a hard time finding much that was clear on Bell’s inequality, or its various more modern versions.

  Then Asher’s book arrived at our library.

  Revelation! Suddenly, all the key results of 30 years of work (several of those results due to Asher) were distilled into beautiful and simple explanations.

  The other parts of the book are just as good.

• One of the originators of the famous Peres-Horodecki criterion for deciding when a quantum state is entangled.
• One of the originators of quantum teleportation.

I didn’t know Asher all that well – we talked more than passingly on only a few occasions – but I have several warm memories of our interactions.

One was in 2000. I had posted a paper to the preprint archive entitled “On the units of bipartite entanglement: is sixteen ounces always equal to one pound?”

I had recently left a job at Caltech when I posted that paper. Caltech runs JPL, who at the time were still very embarassed by the loss of the Mars Lander, due to, of all things, a now-famous mistake in unit conversion.

Shortly after posting the paper, I got a little note in email from Asher that brightened my day and still makes me smile. I post it here because it seems to me very much in Asher’s voice as I knew it:

“Sixteen ounces? One pound?
Don’t people at Caltech know about SI units? Best regards, Asher”