David J. Santos

Quantum authentication of classical messages

Although key distribution is arguably the most studied context on which to apply quantum cryptographic techniques, message authentication, i.e., certifying the identity of the message originator and the integrity of the message sent, can also benefit from the use of quantum resources. Classically, message authentication can be performed by techniques based on hash functions. However, the security of the resulting protocols depends on the selection of appropriate hash functions, and on the use of long authentication keys. In this paper, we e propose a quantum authentication procedure that, making use of just one qubit as the authentication key, allows the authentication of binary classical messages in a secure manner.

Transient analysis of a nonlinear fiber ring resonator

In this letter we study the transient behavior of a nonlinear fiber ring resonator operating both as an optical bistable and as a differential amplifier. The speed of response of the structure is investigated, and some general considerations on the performance of these kinds of devices are presented.

Quantum authentication with unitary coding sets

Abstract A general class of authentication schemes for arbitrary quantum messages is proposed. The class is based on the use of sets of unitary quantum operations in both transmission and reception, and on appending a quantum tag to the quantum message used in transmission. The previous secret between partners required for any authentication is a classical key. We obtain the minimal requirements on the unitary operations that lead to a probability of failure of the scheme less than one. This failure may be caused by someone performing a unitary operation on the message in the channel between the communicating partners, or by a potential forger impersonating the transmitter.

Continuum states and fields in quantum optics

The relation between the continuous-mode quantization scheme used in quantum optics and the quantum system formed by a continuum of standard harmonic oscillators is established. The number and coherent states of this system are shown to be the ones introduced without explicit reference to the continuum by other authors.

Photonic excess noise in a p-i-n photodetector

Abstract We derive an analytical expression for the photonic noise variance of a p - i - n photodetector taking into account the randomness in the shape of the impulse response. The induced excess noise over the quantum limit is computed and the obtained result is contrasted with the standard model of ideal photodetector usually found in the literature.

INSIGHTS AND IMPLICATIONS FROM A BAYESIAN APPROACH TO QUANTUM INFORMATION

Providing quantum theory, and thus quantum information, with some meaning, can only be the result of adopting a well-defined approach to the notion of probability. From a subjectivistic Bayesian approach to the latter, it follows that not only quantum states, but also quantum operations, are structural elements of a subjective nature. Furthermore, we provide a representation of any quantum operation as a stochastic matrix.

Bayesian Intersubjectivity and Quantum Theory

Two of the major approaches to probability, namely, frequentism and (subjectivistic) Bayesian theory, are discussed, together with the replacement of frequentist objectivity for Bayesian intersubjectivity. This discussion is then expanded to Quantum Theory, as quantum states and operations can be seen as structural elements of a subjective nature.

Quantum noise analysis of an amplifying TCRR using a continuous-modes formalism

A quantum-mechanical model of the amplifying two-coupler ring resonator based on the continuous-modes theory of quantum optics is used to show certain noise resonances of the output fields.