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Josephson quantum computing device and integrated circuit using such devices

外国特許コード F110003358
整理番号 A241-47WO
掲載日 2011年6月23日
出願国 アメリカ合衆国
出願番号 65864705
公報番号 20090261319
公報番号 8284585
出願日 平成17年7月25日(2005.7.25)
公報発行日 平成21年10月22日(2009.10.22)
公報発行日 平成24年10月9日(2012.10.9)
国際出願番号 JP2005013585
国際公開番号 WO2006011451
国際出願日 平成17年7月25日(2005.7.25)
国際公開日 平成18年2月2日(2006.2.2)
優先権データ
  • 特願2004-219284 (2004.7.27) JP
  • 特願2004-375008 (2004.12.24) JP
  • 2005JP013585 (2005.7.25) WO
発明の名称 (英語) Josephson quantum computing device and integrated circuit using such devices
発明の概要(英語) A Josephson quantum computing device and an integrated circuit using Josephson quantum computing devices which can realize a NOT gate operation controlled with 2 bits will be provided.
The Josephson quantum computing device (1) comprises: a superconducting ring member (10) having a &pgr;-junction (6) and a 0-junction (7); and a quantum state detecting member (20) constituted by a superconducting quantum interference device arranged outside of the superconducting ring member, wherein a bonding and an antibonding state brought about by a tunneling effect between a |↑> and a |↓> state as two states degenerate in energy of the superconducting ring member (10) are regarded as quantum bits.
The bonding and antibonding states as the quantum bits are read out by the quantum state detecting member (20).
The two bit controlled NOT gate operation can be performed by the two quantum bits comprising said quantum bits.
従来技術、競合技術の概要(英語) BACKGROUND ART
The quantum computer is a computer that has an overwhelmingly rapid computing speed in solving particular problems that could not be solved in reality by conventional classical computers.
In the quantum computer, a quantum two-level system called the quantum bit or qubit is utilized to correspond to a bit in a classical computer.
While a number of qubits are used in computation, the most basic operation is carried out by unitary transformation manipulations for any one qubit and with a quantum operating device that reads out the qubit manipulated.
In a solid-state electronic device, physical states proposed as usable for such qubits are superconducting, electronic and nuclear spin states.
At the outset, an explanation is given of basic particulars of qubits.
In general, if there are two physical states corresponding, respectively, to |0> and |1>, a state of superposition given by their superposition |0>+|1> functions as a qubit.
Thus, while a classical bit is either 0 or 1, qubits other than |0> or |1> state include innumerable states intermediate between |0> and |1> and further those which are different in phase.
It is called unitary transformation to let such a certain state |s> change to another state |s'>.
Qubits constituting a quantum computer need to equip the following four functions:
The first is initialization, requiring a means to set an initial state of a qubit as a well defined one, e.g., |0> or |1>.
The second is controlling a state (quantum operating gate), requiring a means to unitarily transform a prepared initial state (e.g., |0> or |1>) to any state of superimposition as desired |s>.
The third is to read out, requiring a detecting means to measure a unitarily transformed state |s>, namely to determine the values of amplitudes of |0> and |1>.
The fourth relates to expandability, requiring the conditional state control (controlled NOT gate) first on two bits and then requiring expansion by integration further to a number of qubits.
As quantum operating devices using superconducting qubits, there is a proposal to utilize electron pair boxes as two superconducting states having different charge states.
There is also a proposal to utilize a superconducting quantum interference device (SQUID) to measure superconducting states having states different in phase.
In non-patent references 1 to 3 listed below, a theoretical proposal of a qubit consisting of a superconducting ring with three Josephson junctions and the detection of bonding and antibonding states in the proposed qubit have been reported.
In this qubit, if an external magnetic field corresponding to half a unit magnetic flux is applied to the superconducting ring, two states degenerate in energy are realized.
As a result, a bonding or an antibonding state that is any arbitrary state of superposition as desired of the second function mentioned above for qubits is formed.
In such degenerate states, currents mutually opposite in direction flow through the superconducting ring.
Thus, the superconducting ring to which an external magnetic field near the magnetic field corresponding to one half the unit magnetic flux is applied is irradiated with a microwave corresponding to an energy difference between the bonding and antibonding states, and a superconducting quantum interference device disposed around the quantum bit constituted of the superconducting ring is used to indirectly measure current flowing through the superconducting ring, thereby detecting if the state is bonding or antibonding.
In non-patent reference 4 in the list below, a theoretical proposal has been made on a qubit using a Josephson junction formed of an anisotropic (d-wave) superconductor and an isotropic (s-wave) superconductor.
In this Josephson junction, by the effect of the anisotropic (d-wave) superconductor, its free energy becomes the minimum and its system becomes stable if the phase difference of the superconducting gap is +-pi /2.
The proposed qubit is used to arbitrarily superpose the bonding and antibonding states formed of these two degenerate states as the second function mentioned above for qubits.
In non-patent reference 5 in the list below, there have been reported a theoretical proposal on a qubit constituted by a superconducting ring with one ferromagnetic pi -junction and four 0-junctions and reference to the qubit using an anisotropic superconductor discussed in non-patent reference 3.
It is shown that the free energy of this system has its minimum when the phase difference of the superconducting gap is +-pi /2, since the pi junction large in the proportion of Josephson function is disposed between the two pairs of 0-junctions.
The proposed qubit is used to arbitrarily superpose the bonding and antibonding states formed of these two degenerate states as the second function mentioned above for qubits.
Nonpatent Reference 1: J. E. Mooij and five others, "Josephson Persistent-Current Qubit", SCIENCE, vol. 285, pp. 1036 (1999);
Nonpatent Reference 2: Caspar H. van der Wal and seven others, "Quantum Superposition of Macroscopic Persistent-Current States", SCIENCE, vol. 290, pp. 773 (2000);
Nonpatent Reference 3: I. Chiorescu and three others, "Coherent Quantum Dynamics of a Superconducting Flux Qubit", SCIENCE, vol. 299, pp. 1869 (2003);
Nonpatent Reference 4: Lev B. Ioffe and four others, "Environmentally decoupled sds-wave Josephson junction for quantum computing", Nature, vol. 398, pp. 679 (1999); and
Nonpatent Reference 5: G. Blatter and two others, "Design aspects of superconducting-phase quantum bits", Physical Review B, vol. 63, pp. 174511-1 (2001).

特許請求の範囲(英語) [claim1]
1. A Josephson quantum computing device, characterized in that it comprises: a superconducting ring member with a pi -junction constituted of a Josephson junction and a first 0-junction or a first and a second 0-junctions each of which is constituted of a Josephson junction; and
a quantum state detecting member constituted by a superconducting quantum interference device arranged outside of said superconducting ring member, wherein:
a bonding and an antibonding state brought about by a tunneling effect between a | (up arrow) > and a |.down arrow dbl.> state as two states degenerate in energy of said superconducting ring member are regarded as quantum bits, and
said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member.
[claim2]
2. The Josephson quantum computing device as set forth in claim 1, characterized in that said superconducting ring member comprises a pair of semicircular superconductors, a ferromagnetic metal sandwiched between adjacent first ends of said superconductors and an insulator sandwiched between adjacent second ends of said superconductors wherein said two superconductors and said ferromagnetic metal together form said pi -junction and said two superconductors and said insulator together form said 0-junction.
[claim3]
3. The Josephson quantum computing device as set forth in claim 1, characterized in that said superconducting ring member comprises a first, a second and a third superconductor which as a whole are disposed in the form of a ring and are strips essentially tri-partitioned of the ring and arranged having three interspaces open between their adjacent ends and a ferromagnetic body and a first and a second insulator with which the three interfaces are filled, respectively, wherein: said first superconductor, said first insulator and said third superconductor together form said first 0-junction,
said second superconductor, said second insulator and said third superconductor together form said second 0 junction, and
said first superconductor, said ferromagnetic body and said second superconductor together form said pi -junction.
[claim4]
4. A Josephson quantum computing device, characterized in that it comprises: a superconducting ring member having a pi -junction and a 0-junction; and
a quantum state detecting member constituted by a superconducting quantum interference device arranged outside of said superconducting ring member, wherein:
a bonding and antibonding state brought about by a tunneling effect between a | (up arrow) > and a |.down arrow dbl.> state as two states degenerate in energy of said superconducting ring member are regarded as quantum bits, and
said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member.
[claim5]
5. The Josephson quantum computing device as set forth in claim 4, characterized in that said superconducting ring member comprises a pair of semicircular superconductors, a ferromagnetic metal sandwiched between adjacent first ends of said superconductors and an insulator sandwiched between adjacent second ends of said superconductors wherein said two superconductors and said ferromagnetic metal together form said pi -junction and said two superconductors and said insulator together form said 0-junction.
[claim6]
6. The Josephson quantum computing device as set forth in claim 4 or claim 5, characterized in that said bonding and antibonding states of said superconducting ring member are controlled by a ratio (gamma ) of Josephson coupling constants at said pi - and 0-junctions.
[claim7]
7. The Josephson quantum computing device as set forth in claim 4 or claim 5, characterized in that said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member upon applying thereto an external magnetic field.
[claim8]
8. The Josephson quantum computing device as set forth in claim 4, characterized in that said bonding and antibonding states as the quantum bits are states that are superposed arbitrarily as desired by a microwave with which said quantum bits are irradiated.
[claim9]
9. An integrated circuit using Josephson quantum computing devices, characterized in that each of said Josephson quantum computing devices comprises: a superconducting ring member having a pi -junction constituted of a Josephson junction and a first 0-junction or a first and a second 0-junction each of which is constituted of a Josephson junction; and
a quantum state detecting member constituted by a superconducting quantum interference device arranged outside of said superconducting ring member, wherein:
a bonding and an antibonding state brought about by a tunneling effect between a | (up arrow) > and a |.down arrow dbl.> state as two states degenerate in energy of said superconducting ring member are regarded as quantum bits, and
said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member.
[claim10]
10. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that said superconducting ring member has a pi -junction constituted of a Josephson junction and a first 0-junction which is constituted of a Josephson junction and comprises a pair of semicircular superconductors, a ferromagnetic metal sandwiched between respective and adjacent first ends of said superconductors and an insulator sandwiched between respective and adjacent second ends of said superconductors wherein said two superconductors and said ferromagnetic metal together form said pi -junction and said two superconductors and said insulator together form said 0-junction.
[claim11]
11. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that: said superconducting ring member has a pi -junction constituted of a Josephson junction and a first and a second 0-junction each of which is constituted of a Josephson junction and comprises a first, a second and a third superconductor which as a whole are disposed in the form of a ring and are strips essentially tri-partitioned of the ring and arranged having three interspaces open between their adjacent ends and a ferromagnetic body and a first and a second insulator with which the three interfaces are filled, respectively, wherein:
said first superconductor, said first insulator and said third superconductor together form said first 0-junction,
said second superconductor, said second insulator and said third superconductor together form said second 0 junction, and
said first superconductor, said ferromagnetic body and said second superconductor together form said pi -junction.
[claim12]
12. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that said bonding and antibonding states of said superconducting ring member are controlled by a ratio (gamma ) of Josephson coupling constants at said first and second 0-junctions and said pi -junction.
[claim13]
13. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member upon applying thereto an external magnetic field.
[claim14]
14. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that two such quantum bits adjacent to each other are so arranged as to bring about a magnetic interaction and operates as a controlled NOT gate.
[claim15]
15. The integrated circuit using Josephson quantum computing devices as set forth in claim 9, characterized in that said bonding and antibonding states as said quantum bits are states that are superposed as desired by a microwave with which said quantum bits are irradiated to operate as a controlled NOT gate.
  • 発明者/出願人(英語)
  • MAEKAWA SADAMICHI
  • YAMASHITA TARO
  • TAKAHASHI SABURO
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 365/129
  • 257/34
  • 365/106
参考情報 (研究プロジェクト等) CREST Creation of Nanodevices and System Based on New Physical Phenomena and Functional Principles AREA
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