6,183 research outputs found
Small Pseudo-Random Families of Matrices: Derandomizing Approximate Quantum Encryption
A quantum encryption scheme (also called private quantum channel, or state
randomization protocol) is a one-time pad for quantum messages. If two parties
share a classical random string, one of them can transmit a quantum state to
the other so that an eavesdropper gets little or no information about the state
being transmitted. Perfect encryption schemes leak no information at all about
the message. Approximate encryption schemes leak a non-zero (though small)
amount of information but require a shorter shared random key. Approximate
schemes with short keys have been shown to have a number of applications in
quantum cryptography and information theory.
This paper provides the first deterministic, polynomial-time constructions of
quantum approximate encryption schemes with short keys. Previous constructions
(quant-ph/0307104) are probabilistic--that is, they show that if the operators
used for encryption are chosen at random, then with high probability the
resulting protocol will be a secure encryption scheme. Moreover, the resulting
protocol descriptions are exponentially long. Our protocols use keys of the
same length as (or better length than) the probabilistic constructions; to
encrypt qubits approximately, one needs bits of shared key.
An additional contribution of this paper is a connection between classical
combinatorial derandomization and constructions of pseudo-random matrix
families in a continuous space.Comment: 11 pages, no figures. In Proceedings of RANDOM 2004, Cambridge, MA,
August 200
Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off
Transparent conducting oxides have recently gained great attention as
CMOS-compatible materials for applications in nanophotonics due to their low
optical loss, metal-like behavior, versatile/tailorable optical properties, and
established fabrication procedures. In particular, aluminum doped zinc oxide
(AZO) is very attractive because its dielectric permittivity can be engineered
over a broad range in the near infrared and infrared. However, despite all
these beneficial features, the slow (> 100 ps) electron-hole recombination time
typical of these compounds still represents a fundamental limitation impeding
ultrafast optical modulation. Here we report the first epsilon-near-zero AZO
thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation
and recombination time below 1 ps) and an outstanding reflectance modulation up
to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength
of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the
result of a low temperature fabrication procedure promoting oxygen vacancies
and an ultra-high carrier concentration. As a proof-of-concept, an all-optical
AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and
operating at THz frequencies is numerically demonstrated. Our results overcome
the traditional "modulation depth vs. speed" trade-off by at least an order of
magnitude, placing AZO among the most promising compounds for
tunable/switchable nanophotonics.Comment: 14 pages, 9 figures, 1 tabl
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