451 research outputs found
Nonlinear coupling of nano mechanical resonators to Josephson quantum circuits
We propose a technique to couple the position operator of a nano mechanical
resonator to a SQUID device by modulating its magnetic flux bias. By tuning the
magnetic field properly, either linear or quadratic couplings can be realized,
with a discretely adjustable coupling strength. This provides a way to realize
coherent nonlinear effects in a nano mechanical resonator by coupling it to a
Josephson quantum circuit. As an example, we show how squeezing of the nano
mechanical resonator state can be realized with this technique. We also propose
a simple method to measure the uncertainty in the position of the nano
mechanical resonator without quantum state tomography
Three and Four-Body Interactions in Spin-Based Quantum Computers
In the effort to design and to construct a quantum computer, several leading
proposals make use of spin-based qubits. These designs generally assume that
spins undergo pairwise interactions. We point out that, when several spins are
engaged mutually in pairwise interactions, the quantitative strengths of the
interactions can change and qualitatively new terms can arise in the
Hamiltonian, including four-body interactions. In parameter regimes of
experimental interest, these coherent effects are large enough to interfere
with computation, and may require new error correction or avoidance techniques.Comment: 5 pages incl. 4 figures. To appear in Phys. Rev. Lett. For an
expanded version including detailed calculations see
http://xxx.lanl.gov/abs/cond-mat/030201
Simple proof of equivalence between adiabatic quantum computation and the circuit model
We prove the equivalence between adiabatic quantum computation and quantum
computation in the circuit model. An explicit adiabatic computation procedure
is given that generates a ground state from which the answer can be extracted.
The amount of time needed is evaluated by computing the gap. We show that the
procedure is computationally efficient.Comment: 5 pages, 2 figures. v2: improved gap estimates and added some more
detail
Mimicking Time Evolution within a Quantum Ground State: Ground-State Quantum Computation, Cloning, and Teleportation
Ground-state quantum computers mimic quantum mechanical time evolution within
the amplitudes of a time-independent quantum state. We explore the principles
that constrain this mimicking. A no-cloning argument is found to impose strong
restrictions. It is shown, however, that there is flexibility that can be
exploited using quantum teleportation methods to improve ground-state quantum
computer design.Comment: 10 pages, 7 figure
Universal computation by multi-particle quantum walk
A quantum walk is a time-homogeneous quantum-mechanical process on a graph
defined by analogy to classical random walk. The quantum walker is a particle
that moves from a given vertex to adjacent vertices in quantum superposition.
Here we consider a generalization of quantum walk to systems with more than one
walker. A continuous-time multi-particle quantum walk is generated by a
time-independent Hamiltonian with a term corresponding to a single-particle
quantum walk for each particle, along with an interaction term. Multi-particle
quantum walk includes a broad class of interacting many-body systems such as
the Bose-Hubbard model and systems of fermions or distinguishable particles
with nearest-neighbor interactions. We show that multi-particle quantum walk is
capable of universal quantum computation. Since it is also possible to
efficiently simulate a multi-particle quantum walk of the type we consider
using a universal quantum computer, this model exactly captures the power of
quantum computation. In principle our construction could be used as an
architecture for building a scalable quantum computer with no need for
time-dependent control
Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping
We propose a method to dynamically generate and control the flow of
spin-entangled electrons, each belonging to a spin-singlet, by means of
adiabatic quantum pumping. The pumping cycle functions by periodic time
variation of localized two-body interactions. We develop a generalized approach
to adiabatic quantum pumping as traditional methods based on scattering matrix
in one dimension cannot be applied here. We specifically compute the flow of
spin-entangled electrons within a Hubbard-like model of quantum dots, and
discuss possible implementations and identify parameters that can be used to
control the singlet flow.Comment: 4 pages, 3 figure
Chemical Properties of Sago Grub (Rhynchophorus ferrugineus) Protein Concentrate With Different Initial Drying Method
The sago grub (Rhychophorus ferrugineus) is a kind of edible insect which can be utilized as an substitute source of protein in the form of concentrates. The extraction process of protein concentrate requires a proper drying technique for the starting material. This study was intended to determine the appropriate initial drying method for sago grub to produce protein concentrates with good chemical properties. In this study, cabinet dryer, sun, and oven drying methods were used to extract sago caterpillar protein concentrate with a block randomized design. The variables observed were the moisture, ash, protein, and fat contents of the sago grub protein concentrate. The results demonstrated that cabinet dryers are the most appropriate drying method for producing protein concentrate with the best chemical and functional characteristics. The drying method of the cabinet dryer produces a protein concentrate with a moisture content of 23%, an ash content of 11.26%, a protein content of 55.37%, and a fat content of 7.67%
Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms
We present a circuit QED experiment in which a separate transmission line is
used to address a quasi-lumped element superconducting microwave resonator
which is in turn coupled to an Al/AlO/Al Cooper-pair box (CPB) charge
qubit. In our measurements we find a strong correlation between the measured
lifetime of the CPB and the coupling between the qubit and the transmission
line. By monitoring perturbations of the resonator's 5.44 GHz resonant
frequency, we have measured the spectrum, lifetime (), Rabi, and Ramsey
oscillations of the CPB at the charge degeneracy point while the CPB was
detuned by up to 2.5 GHz . We find a maximum lifetime of the CPB was s for to 4.5 GHz. Our measured 's are consistent with
loss due to coupling to the transmission line, spurious microwave circuit
resonances, and a background decay rate on the order of
s of unknown origin, implying that the loss tangent in the AlO
junction barrier must be less than about at 4.5 GHz, about 4
orders of magnitude less than reported in larger area Al/AlO/Al tunnel
junctions
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