10 research outputs found
Quantum Communication Protocol Employing Weak Measurements
We propose a communication protocol exploiting correlations between two
events with a definite time-ordering: a) the outcome of a {\em weak
measurement} on a spin, and b) the outcome of a subsequent ordinary measurement
on the spin. In our protocol, Alice, first generates a "code" by performing
weak measurements on a sample of N spins.
The sample is sent to Bob, who later performs a post-selection by measuring
the spin along either of two certain directions. The results of the
post-selection define the "key', which he then broadcasts publicly. Using both
her previously generated code and this key, Alice is able to infer the {\em
direction} chosen by Bob in the post-selection. Alternatively, if Alice
broadcasts publicly her code, Bob is able to infer from the code and the key
the direction chosen by Alice for her weak measurement. Two possible
experimental realizations of the protocols are briefly mentioned.Comment: 5 pages, Revtex, 1 figure. A second protocol is added, where by a
similar set of weak measurement Alice can send, instead of receiving, a
message to Bob. The security question for the latter protocol is discusse
Weak measurement of arrival time
The arrival time probability distribution is defined by analogy with the
classical mechanics. The difficulty of requirement to have the values of
non-commuting operators is circumvented using the concept of weak measurements.
The proposed procedure is suitable to the free particles and to the particles
subjected to an external potential, as well. It is shown that such an approach
imposes an inherent limitation to the accuracy of the arrival time
determination.Comment: 3 figure
Sequential quantum secret sharing in a noisy environment aided with weak measurements
In this work we give a -threshold protocol for sequential secret
sharing of quantum information for the first time.
By sequential secret sharing we refer to a situation where the dealer is not
having all the secrets at the same time, at the beginning of the protocol;
however if the dealer wishes to share secrets at subsequent phases she/he can
realize it with the help of our protocol. First of all we present our protocol
for three parties and later we generalize it for the situation where we have
parties.
Further in a much more realistic situation, we consider the sharing of qubits
through two kinds of noisy channels, namely the phase damping channel (PDC) and
the amplitude damping channel (ADC). When we carry out the sequential secret
sharing in the presence of noise we observe that the fidelity of secret sharing
at the iteration is independent of the effect of noise at the
iteration. In case of ADC we have seen that the average fidelity
of secret sharing drops down to which is equivalent to a random
guess of the quantum secret. Interestingly, we find that by applying weak
measurements one can enhance the average fidelity. This increase of the average
fidelity can be achieved with certain trade off with the success probability of
the weak measurements.Comment: 9 pages, 5 figures, To appear in European Physical Journal