56,141 research outputs found
Hardware authentication based on PUFs and SHA-3 2nd round candidates
Security features are getting a growing interest in microelectronics. Not only entities have to authenticate in the context of a high secure communication but also the hardware employed has to be trusted. Silicon Physical Unclonable Functions (PUFs) or Physical Random Functions, which exploits manufacturing process variations in integrated circuits, have been used to authenticate the hardware in which they are included and, based on them, several cryptographic protocols have been reported. This paper describes the hardware implementation of a symmetric-key authentication protocol in which a PUF is one of the relevant blocks. The second relevant block is a SHA-3 2nd round candidate, a Secure Hash Algorithm (in particular Keccak), which has been proposed to replace the SHA-2 functions that have been broken no long time ago. Implementation details are discussed in the case of Xilinx FPGAs.Junta de AndalucĂa P08-TIC-03674Comunidad Europea FP7-INFSO-ICT-248858Ministerio de Ciencia y TecnologĂa TEC2008-04920 y DPI2008-0384
Spin quantum computation in silicon nanostructures
Proposed silicon-based quantum-computer architectures have attracted
attention because of their promise for scalability and their potential for
synergetically utilizing the available resources associated with the existing
Si technology infrastructure. Electronic and nuclear spins of shallow donors
(e.g. phosphorus) in Si are ideal candidates for qubits in such proposals
because of their long spin coherence times due to their limited interactions
with their environments. For these spin qubits, shallow donor exchange gates
are frequently invoked to perform two-qubit operations. We discuss in this
review a particularly important spin decoherence channel, and bandstructure
effects on the exchange gate control. Specifically, we review our work on donor
electron spin spectral diffusion due to background nuclear spin flip-flops, and
how isotopic purification of silicon can significantly enhance the electron
spin dephasing time. We then review our calculation of donor electron exchange
coupling in the presence of degenerate silicon conduction band valleys. We show
that valley interference leads to orders of magnitude variations in electron
exchange coupling when donor configurations are changed on an atomic scale.
These studies illustrate the substantial potential that donor electron/nuclear
spins in silicon have as candidates for qubits and simultaneously the
considerable challenges they pose. In particular, our work on spin decoherence
through spectral diffusion points to the possible importance of isotopic
purification in the fabrication of scalable solid state quantum computer
architectures. We also provide a critical comparison between the two main
proposed spin-based solid state quantum computer architectures, namely, shallow
donor bound states in Si and localized quantum dot states in GaAs.Comment: 14 pages. Review article submitted to Solid State Communication
Control of valley dynamics in silicon quantum dots in the presence of an interface step
Recent experiments on silicon nanostructures have seen breakthroughs toward
scalable, long-lived quantum information processing. The valley degree of
freedom plays a fundamental role in these devices, and the two lowest-energy
electronic states of a silicon quantum dot can form a valley qubit. In this
work, we show that a single-atom high step at the silicon/barrier interface
induces a strong interaction of the qubit and in-plane electric fields, and
analyze the consequences of this enhanced interaction on the dynamics of the
qubit. The charge densities of the qubit states are deformed differently by the
interface step, allowing non-demolition qubit readout via valley-to-charge
conversion. A gate-induced in-plane electric field together with the interface
step enables fast control of the valley qubit via electrically driven valley
resonance. We calculate single- and two-qubit gate times, as well as relaxation
and dephasing times, and present predictions for the parameter range where the
gate times can be much shorter than the relaxation time and dephasing is
reduced.Comment: 12 pages, 6 figure
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