Trouble for quantum cryptography researchers ?

It isn't too late for me to realize that success of one field of science may sometimes have detrimental effect on another.

One can realize the conflict between security researchers and computer forensic researchers. One is devoted to make things completely secure from outsiders, while the other desires to peek into users' data as much as possible. I met one guy during a Trusted Computing (TC) workshop, who was researching computer forensic. After attending some talks, he was worried that success of the TC platform could mean insurmoutnable challenge to his field.

Recently, i was made aware of quantum cryptography, wherein quantum mechanic is utilised to make man-in-the-middle attack impossible. Quantum particle can be used to provide absolute secrecy for key transportation. Basically, a quantum particle can be in a bizzare state call superposition, which means being in two states (A and B) at the same time. However, this state will collapse to a classical, physical state (A or B) when we measure or look into it, and it will stay there forever.

Cryptography researchers exploit this properties to transport encryption key between two participants (namely Alice and Bob). The current transportation means is electronic bit, which is either 0 or 1. An eavesdropper Eve can intercept the bits without being noticed by either Alice or Bob. Using a quantum bit (or qBit) being in the superposition state to transfer data, if Eve intercept the qBit (i.e. look/measure it), the qBit would collapse into one state, and will be easily recognized by both Alice and Bob. As the consequence, they are now aware of the eavesdropper's activity and would be likely to stop the transaction. With quantum mechanics, no one can peek into the particle's state without destroying it.

It all sounds like the ultimate solution for cryptography. Until recently, some scientists at the University of California, Santa Barbara revealed the possibility of conducting a weak measurement of quantum particles without destroying its superposition state. They realized that the collapsing process happens in a finite period of time, rather than absolutely instant. Weak measurement can undo any damange.

If this proves successfull, it may signal the end to quantum cryptographic science. An eavesdropper could intercepts messages without being notice. Well, we are back to the first place again !!