[Marxism] quantum information: putting certainty in the bank

Louis Proyect lnp3 at panix.com
Thu Aug 11 12:13:28 MDT 2005


(Les, for some reason this bounced.)

The Subject line is the title of a review of a paper published last week on 
the topic of quantum information theory. its an interesting title for a 
couple reasons.

classical information theory was developed in the late 1940's, by Shannon

   <http://www.ieee.org/organizations/history_center/legacies/shannon.html>http://www.ieee.org/organizations/history_center/legacies/shannon.html

(his major paper was done while at AT&T's Bell Labs) and others, in part as 
a means to analyze the capacity of information transmission schemes to 
handle data flows:

    <http://en.wikipedia.org/wiki/Information_theory>http://en.wikipedia.org/wiki/Information_theory

by introducing statistical concepts like uncertainty and entropy, insight 
was gained into transmission processes based on classical physical grounds. 
Schumacher (based on von Neumann's quantum entropy)  among others extended 
this work into the quantum realm, but these  results were thought to be 
highly unsatisfactory for several reasons, e.g.,

      <http://prola.aps.org/abstract/PRA/v63/i2/e022113>http://prola.aps.org/abstract/PRA/v63/i2/e022113 
,

one of the chief complaints being that quantum systems would admit negative 
uncertainty. what the hell could that mean???

which brings us back to the current paper under review. it's authors were 
able to construct an analysis which makes sense of negative uncertainty 
(the review article calls this "more than certain") in terms of a quantum 
condition called entanglement (i've written briefly on this, check the 
archives, or google is your friend). from the review:

n practice, if the receiver is more than certain, the sender doesn't need 
to transmit any qubits at all for the receiver to be able to decipher the 
message. So the receiver can put some certainty in the bank for a rainy 
day, in the form of extra entanglement with the sender that could be used 
to reduce the receiver's uncertainty about future messages. Entanglement is 
such a strong form of correlation that it can actually be used to send 
qubits from the sender to the receiver using a procedure known as quantum 
teleportation[6]. On the accounting ledger, therefore, having stored 
entanglement is almost as good as being able to communicate.


since classical systems do not exhibit entanglement (that's a long story in 
itself), we have another example of how contemporary quantum theory can be 
seen to oppose the notion that quantum mechanics is all about uncertainty 
and unknowability -- interesting reason #1.

interesting reason #2 is the "bank" is the review's title. a sizable 
fraction of current work in quantum information theory relates to quantum 
cryptography, currently the prayer of financial systems worldwide for 
providing bullet-proof security to financial transactions. this relates in 
part to quantum uncertainty, in that any attempt to sniff out quantum 
transmission of information MUST of necessity alter the state of that 
information, and being a detectable alteration, means no one can eavesdrop 
un-noticed on said transactions. if you still believe quantum mechanics is 
in error, your future in financial thievery looks bright.


i am certainly,
les schaffer



p.s. an interesting article on info theory and creationism:

   <http://home.mira.net/~reynella/debate/informat.htm>http://home.mira.net/~reynella/debate/informat.htm


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