Category: Information and Communication

Here is another variant of the QKD protocol, due to Ekert [32], which makes use of correlated quantum pairs as a resource shared between Alice and Bob. For each key, Bob generates entangled photons and sends one to Alice. 2 Locally each performs a measurement randomly, according to random bit strings m A and m…

The vulnerability of any cryptosystem needs to be subjected to stringent tests before it can be implemented. In fact the very growth of new and efficient cryptographic schemes depends a lot on the input of cryptanalysts, who make a thorough study of possible loopholes and susceptibility to attacks. A study of possible methods that endanger…

The most spectacular successes of quantum information processing tech- niques have been in the field of cryptography, the science of secret message exchange. 1 The reason why Shor’s algorithm shot into prominence and major players started funding quantum computing research was the challenge it of- fered to currently trusted schemes of data encryption, particularly the…

An interesting aspect of quantum information transfer is how one can actually transfer two classical bits of information while physically transmitting only one qubit. This process seems to involve compressing two bits into one qubit and is accordingly called dense coding. The key to the process is the use of entanglement. This protocol preceded and…

As an illustration of the power of entanglement as a resource, we examine the rather dramatically titled protocol of quantum state teleportation. This idea was first introduced by Bennett in 1993 [6]. The teleportation problem is the following: Alice needs to transfer to Bob (at a distant location) an unknown qubit |ψi generically denoted by…

As we have seen in Chapter 4, multi-qubit systems can exist in correlated states known as entangled states. In computing algorithms, entanglement is implicit, but nowhere is it more dramatically useful than in protocols for com- munication, where quantum correlations are exploited for security of commu- nication as well as for coding efficiency. This quantum…

The most successful practical applications of quantum mechanics in informa- tion theory have been in the field of communication. This is a very old field that has taken inputs from engineering, pure mathematics and computer science apart from physics. It is only natural that application of quantum techniques here should be among the first to…