Electricity: measuring and testing – Particle precession resonance
Reexamination Certificate
1999-02-16
2001-04-17
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
C324S307000
Reexamination Certificate
active
06218832
ABSTRACT:
TECHNICAL FIELD
This invention relates to quantum computing, and more particularly to nuclear magnetic resonance quantum computing (NMRQC).
BACKGROUND OF THE INVENTION
Quantum computing was theoretically developed by Feynman (
Optics News,
Feb. 1, 1985) and Deutsch (
Proc. Royal Soc. London
A400, 97 (1985)). Quantum algorithms for these theoretical machines were developed by Grover (
Phys. Rev. Lett.
79, 4709 (1997)) to search unsorted databases faster than is possible with classical computers, and by Shor (
Proc.
35
th Ann. Symp. on Found. of Computer Science,
IEEE Comp. Soc. Press, Los Alamitos, Calif. 1994) to factor numbers and calculate discrete logarithms. Early experimental implementations of quantum computers used ion traps (Cirac and Zoller,
Phys. Rev. Lett.
74, 4091 (1995); Monroe et. al,
Phys. Rev. Lett.
75, 4714 (1995)) and optical systems (Turchette et. al.,
Phys. Rev. Lett.
75, 4710 (1995)) but were able to implement only a single logic gate, one of many that would be required to implement an algorithm.
A significant theoretical advance in quantum computing came when the means for performing quantum computation using nuclear magnetic resonance (NMR) techniques was developed by Gershenfeld and Chuang (
Science
275, 350 (1997)), and independently by Cory, Fahmy, and Havel (
Proc. Nat. Acad. Sci.
94, 1634 (1997)). The NMR technique has successfully been used to demonstrate the operation of two-bit quantum algorithms for searching (Chuang, Gershenfeld, and Kubinec,
Phys. Rev. Left.
80, 3408 (1998)) and period-finding (Chuang, Vandersypen, Zhou, Leung, and Lloyd,
Nature
393, 143 (1998)).
To date, all of the efforts in NMR quantum computing (NMRQC) have involved the use of isotropic liquid solvents, into which molecules specifically suited for carrying out quantum computations are dissolved. Isotropic liquid solvents allow the molecules to tumble isotropically, and average the dipolar interactions to zero. The couplings among the spins that are required for quantum computation are thus scalar in nature. The use of isotropic liquid solvents in NMRQC also results in long coherence times, which means that there is a significant amount of time to perform a computation before external forces disrupt or affect the coupling of the nuclear spins. It has been understood that these features are highly desirable, and that solids, which have long range dipolar couplings, cause rapid decoherence and therefore offer only very reduced operation times when used for quantum computation (Chuang, Gershenfeld, Kubinec, and Leung,
Proc. Royal Soc. London
A (1988) 454, 447). Furthermore, it is known in the art that the advantages of using dipolar couplings in solids for NMRQC operations are outweighed by the disadvantages (W. S. Warren,
Science
277, 1688, 1997).
However, the use of liquid solvents strongly limits the clock rate and thus the computation speed of NMR quantum computers because the requisite coupling among the nuclear spins that persists in solution, the so-called scalar coupling, is small. NMR quantum computers based on liquid solvents also require long waiting times between computations for reinitialization because of the long time required for buildup of the requisite longitudinal nuclear spin magnetization.
The use of liquid crystals as a solvent for NMR experiments was developed for retaining and extracting information from the dipolar interactions among nuclei in the dissolved molecules (A.Saupe and G. Englert,
Phys. Rev. Lett.
11, 462 (1963). In contrast with isotropic liquid solvents, liquid crystal solvents impede the tumbling of dissolved molecules in such a way that the molecules become partially oriented. The result on the NMR spectra is that dipolar couplings between nuclear spins that are averaged to zero in isotropic liquid solvents are observed in liquid crystal solvents. However, liquid crystals have not been used as solvents for NMRQC. This is because it was believed that liquid crystal solvents which induce dipolar couplings would require unduly complex implementation of NMRQC algorithms.
What is needed is a NMRQC system that increases the computation speed and reduces the re-initialization time over NMRQC systems that rely on liquid solvents.
SUMMARY OF THE INVENTION
The present invention is a method for performing NMRQC wherein the quantum computing molecules are dissolved in a liquid crystal. The dissolution of the quantum computing molecules in a liquid crystal solvent removes the limitation on the clock speed of an NMR quantum computer, which was previously determined by the size of the magnetic couplings between the spins in the atoms of the quantum computing molecules dissolved in an isotropic liquid. The method allows implementation of more complex NMRQC algorithms which require execution of many logic gates over the duration of a decoherence time. The method allows NMRQC clock frequencies to be increased by at least an order of magnitude beyond those achievable using isotropic liquid solvents. The method also decreases the reinitialization times for a NMR quantum computer without decreasing the computational capability of the molecular systems. The method makes possible the use of new molecules for NMR quantum computation.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.
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patent: 5940193 (1999-08-01), Hotaling et al.
patent: 6081882 (2000-06-01), Gossett
Feynman, “Quantum Mechanical Computers”, Optics News Feb. 1, 1995, pp. 11-20.
Cirac et al.,“Quntum Computations with Cold Trapped Ions”, Physical Review Letters, vol. 74, No. 20, May 15, 1995, pp. 4091-4094.
Deutsch, “Quantum theory, the Church-Turing principle and the universal quantum computer”, Proc. Royal Society London, vol. 400 1985, pp. 97-117.
Grover, “Quntum Computers Can Search Arbitrarily Large Databases by a Single Query”, Physical Review Letters, vol. 79, No. 23, Dec. 7, 1997, pp. 4709-4712.
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Turchette et al. “Measurement of Conditional Phase Shifts for Quantum Logic”, Physical Review Letters, vol. 75, No. 25, Dec. 18, 1995, pp. 4710-4713.
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Cory et al., “Ensemble Quantum Computing by NMR Spectroscopy”, The National Academy of Sciences of the USA, vol. 94, Mar. 1997 Computer Sciences, pp. 1634-1639.
Chuang et al.,“Experimental Implementation of Fast Quantum Searching”, Physical Review Letters, vol. 80, No. 15, Apr. 13, 1998, pp. 3408-3411.
Chuang et al., “Experimental Realization of a Quantum Algorithm”, Nature vol. 393, May 14, 1998, pp. 143-146.
Chuang et al., “Bulk Quantum Computation with Nuclear Magnetic Resonance: theory and experiment”, Proc. Royal Society London, 1998, pp. 454, 447-467.
Warren et al., “The Usefulness of NMR Quantum Computing”, Science vol. 277, Sep. 12, 1997, pp. 1688-1690.
Saupe et al.,“High-Resolution Nuclear Magnetic Resonance Spectra of Orientated Molecules”, Physical Review Letters, vol. 11, No. 10, Nov. 15, 1963, pp. 462-464.
Gershenfeld et al., “Quntum Computing with Molecules”, Scientific American, Jun. 1998, pp.66-71.
Morris et al., “Enhancement of Nuclear Magnetic Resonance Signals by Polarization Transfer”, Journal of the American Chem. Soc., 101:3, Jan. 31, 1979, pp. 760-762.
Chuang Isaac Liu
Sherwood Mark Hull
Yannoni Costantino Sheldon
Arana Louis
Berthold Thomas R.
International Business Machines - Corporation
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