8,916 research outputs found
High Dynamic Range RF Front End with Noise Cancellation and Linearization for WiMAX Receivers
This research deals with verification of the high dynamic range for a heterodyne radio frequency (RF) front end. A 2.6 GHz RF front end is designed and implemented in a hybrid microwave integrated circuit (HMIC) for worldwide interoperability for microwave access (WiMAX) receivers. The heterodyne RF front end consists of a low-noise amplifier (LNA) with noise cancellation, an RF bandpass filter (BPF), a downconverter with linearization, and an intermediate frequency (IF) BPF. A noise canceling technique used in the low-noise amplifier eliminates a thermal noise and then reduces the noise figure (NF) of the RF front end by 0.9 dB. Use of a downconverter with diode linearizer also compensates for gain compression, which increases the input-referred third-order intercept point (IIP3) of the RF front end by 4.3 dB. The proposed method substantially increases the spurious-free dynamic range (DRf) of the RF front end by 3.5 dB
Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs
If strong electron-electron interactions between neighboring Fe atoms mediate
the Cooper pairing in iron-pnictide superconductors, then specific and distinct
anisotropic superconducting energy gaps \Delta_i(k) should appear on the
different electronic bands i. Here we introduce intra-band Bogoliubov
quasiparticle scattering interference (QPI) techniques for determination of
\Delta_i(k) in such materials, focusing on LiFeAs. We identify the three
hole-like bands assigned previously as \gamma, \alpha_2 and \alpha_1, and we
determine the anisotropy, magnitude and relative orientations of their
\Delta_i(k). These measurements will advance quantitative theoretical analysis
of the mechanism of Cooper pairing in iron-based superconductivity
Prescription for experimental determination of the dynamics of a quantum black box
We give an explicit prescription for experimentally determining the evolution
operators which completely describe the dynamics of a quantum mechanical black
box -- an arbitrary open quantum system. We show necessary and sufficient
conditions for this to be possible, and illustrate the general theory by
considering specifically one and two quantum bit systems. These procedures may
be useful in the comparative evaluation of experimental quantum measurement,
communication, and computation systems.Comment: 6 pages, Revtex. Submitted to J. Mod. Op
Dynamics of quantum phase transition: exact solution in quantum Ising model
Quantum Ising model is an exactly solvable model of quantum phase transition.
This paper gives an exact solution when the system is driven through the
critical point at finite rate. The evolution goes through a series of
Landau-Zener level anticrossings when pairs of quasiparticles with opposite
pseudomomenta get excited with probability depending on the transition rate.
Average density of defects excited in this way scales like a square root of the
transition rate. This scaling is the same as the scaling obtained when the
standard Kibble-Zurek mechanism of thermodynamic second order phase transitions
is applied to the quantum phase transition in the Ising model.Comment: misprints corrected; version to appear in Phys.Rev.Let
Nuclear Magnetic Resonance Quantum Computing Using Liquid Crystal Solvents
Liquid crystals offer several advantages as solvents for molecules used for
nuclear magnetic resonance quantum computing (NMRQC). The dipolar coupling
between nuclear spins manifest in the NMR spectra of molecules oriented by a
liquid crystal permits a significant increase in clock frequency, while short
spin-lattice relaxation times permit fast recycling of algorithms, and save
time in calibration and signal-enhancement experiments. Furthermore, the use of
liquid crystal solvents offers scalability in the form of an expanded library
of spin-bearing molecules suitable for NMRQC. These ideas are demonstrated with
the successful execution of a 2-qubit Grover search using a molecule
(CHCl) oriented in a liquid crystal and a clock speed eight
times greater than in an isotropic solvent. Perhaps more importantly, five
times as many logic operations can be executed within the coherence time using
the liquid crystal solvent.Comment: Minor changes. Published in Appl. Phys. Lett. v.75, no.22, 29 Nov
1999, p.3563-356
Programmable quantum gate arrays
We show how to construct quantum gate arrays that can be programmed to
perform different unitary operations on a data register, depending on the input
to some program register. It is shown that a universal quantum gate array - a
gate array which can be programmed to perform any unitary operation - exists
only if one allows the gate array to operate in a probabilistic fashion. The
universal quantum gate array we construct requires an exponentially smaller
number of gates than a classical universal gate array.Comment: 3 pages, REVTEX. Submitted to Phys. Rev. Let
Polymorphic G:G mismatches act as hotspots for inducing right-handed Z DNA by DNA intercalation
DNA mismatches are highly polymorphic and dynamic in nature, albeit poorly characterized structurally. We utilized the antitumour antibiotic CoII(Chro)2 (Chro = chromomycin A3) to stabilize the palindromic duplex d(TTGGCGAA) DNA with two G:G mismatches, allowing X-ray crystallography-based monitoring of mismatch polymorphism. For the first time, the unusual geometry of several G:G mismatches including syn-syn, water mediated anti-syn and syn-syn-like conformations can be simultaneously observed in the crystal structure. The G:G mismatch sites of the d(TTGGCGAA) duplex can also act as a hotspot for the formation of alternative DNA structures with a GC/GA-5' intercalation site for binding by the GC-selective intercalator actinomycin D (ActiD). Direct intercalation of two ActiD molecules to G:G mismatch sites causes DNA rearrangements, resulting in backbone distortion to form right-handed Z-DNA structures with a single-step sharp kink. Our study provides insights on intercalators-mismatch DNA interactions and a rationale for mismatch interrogation and detection via DNA intercalation
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