WO2001010027A1 - Ordinateur quantique utilisant des qubits magnetiques - Google Patents

Ordinateur quantique utilisant des qubits magnetiques Download PDF

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Publication number
WO2001010027A1
WO2001010027A1 PCT/ES1999/000247 ES9900247W WO0110027A1 WO 2001010027 A1 WO2001010027 A1 WO 2001010027A1 ES 9900247 W ES9900247 W ES 9900247W WO 0110027 A1 WO0110027 A1 WO 0110027A1
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WO
WIPO (PCT)
Prior art keywords
magnetic
spin
element according
logical element
states
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PCT/ES1999/000247
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English (en)
Spanish (es)
Inventor
Javier Tejada Palacios
Joan Manel Hernandez Ferras
Enrique Gonzalez Garcia
Eugene M. Chudnovsky
Original Assignee
Javier Tejada Palacios
Joan Manel Hernandez Ferras
Enrique Gonzalez Garcia
Chudnovsky Eugene M
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Javier Tejada Palacios, Joan Manel Hernandez Ferras, Enrique Gonzalez Garcia, Chudnovsky Eugene M filed Critical Javier Tejada Palacios
Priority to AU52910/99A priority Critical patent/AU5291099A/en
Priority to PCT/ES1999/000247 priority patent/WO2001010027A1/fr
Publication of WO2001010027A1 publication Critical patent/WO2001010027A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena

Definitions

  • the present invention concerns logical and data storage elements based on nanometric size structures (particles and molecular aggregate systems, or "clusters”) for the processing and storage of quantum information.
  • the invention is based on a new class of quantum bit or qubit, a magnetic qubit, that is a mesoscopic spin system.
  • the qubit according to the invention consists of a monodomain magnetic unit, of nanometric dimension, generally dielectric, with a high quality factor (QF) of ferromagnetic resonance, in a quantum superposition of the level corresponding to the fundamental state of spin and the level of the first excited state of spin.
  • QF quality factor
  • This magnetic unit is able to improve the magnetic recording density when the operation is performed in a temperature range of the order of the milikelvin.
  • the invention also relates to a logic gate using a series of magnetic qubits deposited on a suitable substrate and a quantum computer based on magnetic qubits organized according to a suitable architecture.
  • the invention also relates to dielectric materials, such as monodomain magnetic particles of nanometric size or magnetic molecular aggregates with a total spin of less than 1,000, suitable for the preparation of said qubits.
  • the invention also relates to a method for operating a quantum computer built on magnetic qubits.
  • Quantum computing has been one of the fields that in recent years has undergone a faster development partly due to its implications in theoretical physics. Today it is one of the important objectives of experimentation in physics and engineering.
  • An element of a quantum computer is a qubit - an object that exists in a quantum superposition of two states cos (x) ⁇ 0> + sin (x) ⁇ 1> (Feynman).
  • the state of a quantum system (usually denoted by
  • the space of a single qubit covers a base consisting of the two possible classic states denoted by
  • each qubit has an infinite number of pure quantum states, characterized by the continuous variable x.
  • the measure of x destroys the qubit while projecting its state on ⁇ 0> or ⁇ 1>.
  • the qubits must be coupled together in a controlled, predetermined manner.
  • Quantum computers if they develop, will be used in different scientific, technological and business disciplines. In physics, for example, applications such as powerful simulations in atomic and nuclear physics, of the electrical, optical and magnetic properties of materials can be anticipated. Indeed, quantum computers, with their quantum dynamics, will be the most suitable machines for such computations, producing fast and reliable responses.
  • a conventional computer looking for an element among a list of N elements, has to examine N / 2 elements so that it has a 50% chance of success.
  • a quantum computer that performed the same task would require only the square root of N stages, since it can examine multiple elements simultaneously (Grover).
  • quantum parallelism is the basis for solving some problems much more quickly with a quantum processor.
  • WO 99/14858 refers to a quantum computer comprising a semiconductor substrate in which donor atoms are introduced to produce a series of donor nuclear spin electron systems with non-zero electronic wave functions inside the core of the core.
  • donor atoms Other references in the specialized literature known to applicants, of possible interest in this field for a better understanding of the principles of the invention are detailed below:
  • the objective of the invention is the exploitation of magnetic systems, operating in a range of milikelvins temperatures and duly shielded with respect to external magnetic fields, for quantum computing.
  • This invention describes a quantum computer based on magnetic qubits, that is, monodomain magnetic particles of nanometric size or molecular aggregates as previously defined. While all molecular aggregates are identical, monodomain magnetic particles may differ in size and shape.
  • domain is described for example in CP Bean and J. D. Livingston J. Appl. Physics, 30, 120 (1959); and BD Cullity. Introduction to Magnetic Materials, Addison-Wesley Publishing Co., Massachusets, (1972), see also The Magnetic Properties of Materials by JE Thomson, Newnes International Monographs on Materials Science an Technology, CRC Press, Cleveland, Ohio 1968.
  • Each magnetic particle of nanometric size, monodomain or molecular aggregate is deposited, first, in a well-controlled area on a dielectric substrate, for example embedded within a solid matrix, and is located inside a quantum elementary device consisting of a superconductive inductive element and a micro-SQUID (microscopic device, superconductor, quantum interference) in sensor functions.
  • a quantum elementary device consisting of a superconductive inductive element and a micro-SQUID (microscopic device, superconductor, quantum interference) in sensor functions.
  • the quantum states of each qubit are manipulated and measured by sending and receiving electromagnetic signals to and from the corresponding set of superconductive inductive element and micro-SQUID.
  • the quantum states of the different particles of nanometric size are mixed / superimposed by the connection of said quantum elementary devices by superconducting lines with Josephson switches.
  • Two sets of quantum states can be used in a magnetic qubit.
  • the first one refers to the situation in which the passage, by tunnel effect, of the spin of the nanometric particles, monodomain, is suppressed.
  • the first excited state of the spin corresponds, in classical terms, to the uniform precession of the magnetic moment of the particle around its axis of anisotropy.
  • This excited state is separated from the fundamental spin state by the energetic distance that is equal to the product of the Planck constant by the ferromagnetic resonance frequency (FMR).
  • the quality factor (QF) in dielectric ferromagnetic materials can be as high as 10 6 , which suggests a very low decoherence rate.
  • the QF of the FMR of pure dielectric ferromagnetic crystals can be as high as one million, well above the QF of one thousand, widely cited as necessary to perform computation at an adequate scale. Although FMR and its QF have not been measured in individual nanometric particles, there is no reason to believe that it should be smaller than in large crystals.
  • the second situation of quantum states corresponds to small magnetic particles or molecular aggregates where the spin passes through the tunnel through the anisotropic barrier.
  • the phenomenon has been considered both theoretically and experimentally by two of the present inventors Chudnowsky E..M. and Tejada J. in the work “Macroscopic Quantum Tunneling of the Magnetic Moment", (Cambridge University Press 1998). In this case, which is illustrated in Fig. 2, the fundamental state of the particle is divided into two states that can be used as states 10) and 1 1).
  • the energy distance of the first situation is of the order of 0.1 K, while in the second situation said energy distance can be controlled by applying the external magnetic field perpendicular to the anisotropic axis of the particle or molecular aggregate. In any case the temperature of the operation must be in the range of the milikelvin.
  • VLSI very high scale integration
  • AFM atomic force microscopy
  • STM scanning effect microscopy tunnel
  • MFM magnetic force microscopy
  • substrates for organizing these magnetic units whether nanoparticles or molecular aggregates in sets of 1, 2 and 3 dimensions can be matrices such as molecular clathrates, porous zeolites, Langmuir-Blodgett epitaxial film films, plastics and nanotubes. Each nanoparticle or molecular aggregate will act as an individual and identifiable qubit.
  • the mixing or superposition between different qubits is achieved in this invention by placing the magnetic units inside a superconductive and micro-SQUID inductive element assembly, and connecting these quantum elementary assemblies or devices to each other by means of superconducting lines such as shown in Fig. 3 of the attached drawings.
  • the change in the magnetic states of any particle will result from the electromagnetic induction of a superconducting current in the set of superconductive and micro-SQUID inductive element that surrounds said magnetic unit. This current will flow to the neighboring assemblies changing the quantum states of the nearby magnetic units.
  • Josephson type connections (schematized as switches) acting as switches will be used.
  • Josephson type joints allow switching between different states in extremely short times. It is feasible to control the interaction between qubits simply by connecting or disconnecting the corresponding superconducting lines that relate them.
  • Logic gates based on magnetic nanometric structures need to maintain consistency during computing time.
  • the effect of decoherence can be diminished by purifying the particles both chemically and isotopically.
  • the particles must be dielectric in order to avoid the decoherence phenomena associated with the conducting electrons.
  • ferro and ferri nanometric particles with an anisotropic field greater than 0.05 T such as CoFe ⁇ O ,,, -Fe ⁇ and BaFe 12 O 19
  • anti-ferromagnetic particles or nanometric molecular aggregates can be used.
  • Examples are ferritin and molecular aggregates of Fe 8 synthesized according to Wiedghardt K., Pohl K, Jibril I and Huttner G. "Angew. Chem. Int. Ed. Engl. (1984) 77 and with a nominal composition [( C 6 H 15 N 3 ) 6 Fe 8 ( ⁇ 3 -O) 2 ( ⁇ 2 -OH) 12 (Br 7 (H 2 O)) Br 8 H 2 ⁇ ] checked by chemical and infrared analysis. 8 the distance between the levels corresponding to the two lowest levels within the magnetic anisotropic wells is around 5K.
  • the quantum states of the particles can be manipulated by combining two techniques:
  • the coupling of magnetic particles to the superconductive and micro-SQUID inductive element assemblies is an ideal arrangement since both the magnetic units (particles or molecular aggregates) and the said assemblies can operate in the same frequency range.
  • the quality factor (QF) of 10 3 -10 6 will make it possible for the proposed computer to perform 10 3 -10 6 operations without applying error correction. By applying the error correction algorithm the number of operations can be drastically increased. DESCRIPTION OF THE DRAWINGS
  • Fig. 1 is a schematic drawing showing the structure of spin levels in the two potential wells associated with the magnetic anisotropy of the nanometric particles
  • Fig. 2 is a schematic drawing showing the structure of spin levels in two potential wells. The breakage of the degeneration of the fundamental state ⁇ due to the tunnel effect is also indicated; and Fig.
  • FIG. 3 is a schematic drawing indicative, in a simplified, convenient form, of a portion of a possible arrangement of magnetic units (nanometric particles or molecular aggregates), as proposed by the invention deposited on a substrate and whose quantum states are properly mixed / superimposed so that they constitute a logical element suitable for a quantum computer;
  • the figure also includes the symbol of the two quantum states of the spin.
  • a plurality (the drawing only represents a minimum part of the arrangement) of magnetic units (1), are surrounded by a set (2) or quantum elementary device that includes a superconductive inductive element and a micro-SQUID, which will generally surround both the magnetic unit, although the micro-SQUID could adopt another alternative arrangement.
  • Said assemblies (2) are interrelated through superconductive inductive lines (3) each of which contains a control switch (4) that can be a Josephson type junction.
  • Each set (2) is connected to lines (5), preferably also superconductors, to measure and manipulate the qubits.
  • the magnetic units are deposited on a non-magnetic dielectric substrate (6) by the techniques already defined that enable a quality factor (QF) that must exceed the QF of the NMR qubit in the milikelvin range .
  • QF quality factor
  • a set of superconductive and micro-SQUID inductive element can, in principle, manipulate the magnetic state of the magnetic unit (1) with a precision of a quantum of magnetic flux.
  • Connecting said assemblies (2) as shown in Fig. 3 will imply mixing or superimposing the states of the different particles (1).
  • the change in the quantum magnetic state of any magnetic unit will result in the generation of an electromagnetic induction in the assembly (2) surrounding said particle (1).
  • This current will flow to the neighboring assemblies (2) changing the quantum states of the corresponding magnetic units (1) that they enclose.
  • Josephson type connections (5) have already been applied as building blocks for classic digital circuits.
  • the advantage of magnetic systems for quantum computing over all the above mentioned proposals is twofold. In the first place, all the elements necessary to build the said quantum computer already exist and have been experimentally tested.

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  • General Engineering & Computer Science (AREA)
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Abstract

L'invention concerne un ordinateur quantique utilisant des qubits magnétiques constitués d'unités magnétiques (1) monodomaine, nanométriques et diélectriques, avec un facteur de qualité de résonnance ferromagnétique élevé, dans une superposition quantique des niveaux de l'état fondamental de spin et du premier état excité de spin, dans une plage de température de milikelvins. Chaque unité magnétique (1) est déposée sur un substrat diélectrique (6) non magnétique, et se trouve à l'intérieur d'un dispositif élémentaire quantique (2) intégrant un élément inductif supraconducteur et un capteur micro-SQUID. Ces unités magnétiques sont associées à des lignes supraconductrices (5). Les états quantiques de chaque qubit sont manipulés et mesurés par émission et réception de signaux électromagnétiques en direction et en provenance du dispositif élémentaire quantique correspondant, les états quantiques des différentes unités magnétiques étant ainsi mélangés/superposés grâce à la connexion desdits dispositifs élémentaires quantiques par des lignes supraconductrices (3) avec des interrupteurs de type jonction de Josephson (4).
PCT/ES1999/000247 1999-07-30 1999-07-30 Ordinateur quantique utilisant des qubits magnetiques WO2001010027A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU52910/99A AU5291099A (en) 1999-07-30 1999-07-30 Quantic computer based on magnetic qubits
PCT/ES1999/000247 WO2001010027A1 (fr) 1999-07-30 1999-07-30 Ordinateur quantique utilisant des qubits magnetiques

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Application Number Priority Date Filing Date Title
PCT/ES1999/000247 WO2001010027A1 (fr) 1999-07-30 1999-07-30 Ordinateur quantique utilisant des qubits magnetiques

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5530263A (en) * 1994-08-16 1996-06-25 International Business Machines Corporation Three dot computing elements
US5768297A (en) * 1995-10-26 1998-06-16 Lucent Technologies Inc. Method for reducing decoherence in quantum computer memory
US5793091A (en) * 1996-12-13 1998-08-11 International Business Machines Corporation Parallel architecture for quantum computers using ion trap arrays
US5838436A (en) * 1997-03-26 1998-11-17 The United States Of America As Represented By The Secretary Of The Air Force Multi-purpose quantum computing
WO1999014858A1 (fr) * 1997-09-17 1999-03-25 Unisearch Limited Ordinateur quantique

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5530263A (en) * 1994-08-16 1996-06-25 International Business Machines Corporation Three dot computing elements
US5768297A (en) * 1995-10-26 1998-06-16 Lucent Technologies Inc. Method for reducing decoherence in quantum computer memory
US5793091A (en) * 1996-12-13 1998-08-11 International Business Machines Corporation Parallel architecture for quantum computers using ion trap arrays
US5838436A (en) * 1997-03-26 1998-11-17 The United States Of America As Represented By The Secretary Of The Air Force Multi-purpose quantum computing
WO1999014858A1 (fr) * 1997-09-17 1999-03-25 Unisearch Limited Ordinateur quantique
WO1999014614A1 (fr) * 1997-09-17 1999-03-25 Unisearch Limited Dispositifs electroniques permettant de mesurer le spin unique d'un electron et d'un noyau

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Publication number Publication date
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