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EP-4736607-A1 - MODULAR QUANTUM DEVICE WITH JOSEPHSON EFFECT

EP4736607A1EP 4736607 A1EP4736607 A1EP 4736607A1EP-4736607-A1

Abstract

The invention relates to a quantum device (1) comprising: • a quantum component with Josephson effect (10) having a modular critical current (le), produced on a first face of a substrate (SUB), and comprising: • a first layer (11) made of a first superconducting material; • a second layer (12) made of a second superconducting material; • a junction structure (20) connecting the first layer (11) to the second layer (11) and comprising a ferromagnetic layer with a heterogeneous domain (13) having at least one first magnetic domain (D1) in a first direction and a second magnetic domain (D2) in a second direction opposite to the first direction; and • control means configured to apply a write current through the ferromagnetic layer with the heterogeneous domain (13) in order to modify the volume distribution of the two magnetic domains in the ferromagnetic layer with the heterogeneous domain (13) in order to modulate the critical current (le).

Inventors

  • TRASTOY QUINTELA, Juan
  • VILLEGAS, Javier
  • MESORACA, Salvatore
  • CRETE, DENIS
  • BRIATICO, Javier

Assignees

  • THALES
  • Centre National de la Recherche Scientifique

Dates

Publication Date
20260506
Application Date
20240628

Claims (15)

  1. CLAIMS 1. Quantum device (1) comprising: - a Josephson effect quantum component (10) having a modulatable critical current (Ic), produced on a first face of a substrate (SUB), and comprising: o a first layer (11) made of a first superconducting material, o a second layer (12) made of a second superconducting material; o a junction structure (20) connecting the first layer (11) to the second layer (12) and comprising a heterogeneous domain ferromagnetic layer (13) having at least a first magnetic domain (D1) in a first direction and a second magnetic domain (D2) in a second direction opposite to the first direction; - control means configured to apply a writing current through the heterogeneous domain ferromagnetic layer (13) to modify the volume distribution of the two magnetic domains in said heterogeneous domain ferromagnetic layer (13) in order to modulate said critical current (Ic).
  2. 2. Quantum device (1) according to claim 1 wherein the thickness of the heterogeneous domain ferromagnetic layer (13) is less than or equal to 10 nm.
  3. 3. Quantum device (1) according to any one of claims 1 or 2 wherein the thickness of the first layer (11) and/or the second layer (12) is between 20nm and 500nm.
  4. 4. Quantum device (1) according to any one of claims 1 to 3 in which the heterogeneous domain ferromagnetic layer (13) forms a strip having a non-zero curvature; said strip extending along a plane (X,Y) parallel to the first face of the substrate (SUB).
  5. 5. Quantum device (1) according to claim 4 in which the heterogeneous domain ferromagnetic layer (13) forms a U-shaped or semi-circular or sinusoidal strip; said strip extending along a plane (X,Y) parallel to the first face of the substrate (SUB).
  6. 6. Quantum device (1) according to any one of claims 1 to 5 in which the junction structure (20) is confined between on the one hand the first layer (11) deposited on the first face of a substrate (SUB) and on the other hand the second layer (12).
  7. 7. Quantum device (1) according to any one of claims 1 to 5 wherein the first layer (11) and the second layer (12) are coplanar; the junction structure (20) resting on at least a part of the first layer (11) and on at least a part of the second layer (12).
  8. 8. Quantum device (1) according to any one of claims 1 to 7 wherein the junction structure (20) further comprises a fixed homogeneous domain ferromagnetic layer (14) disposed between the first layer (C1) and the heterogeneous domain ferromagnetic layer (13).
  9. 9. Quantum device (1) according to claim 8 wherein the junction structure (20) further comprises a magnetic decoupling layer (15) confined between the fixed homogeneous domain ferromagnetic layer (14) and the heterogeneous domain ferromagnetic layer (13).
  10. 10. Quantum device (1) according to any one of claims 8 or 9 wherein the thickness of the fixed homogeneous domain ferromagnetic layer (14) is greater than twice that of the heterogeneous domain ferromagnetic layer (13).
  11. 11. Quantum device (1) according to any one of the preceding claims in which the heterogeneous domain ferromagnetic layer (13) is made of Ni or NiFe or NiCo or CoFeBo or CoPt or LSMO or LCMO.
  12. 12. Flux quantum bit (QB) comprising: - a superconducting loop formed by the quantum device (1) according to any one of the preceding claims; - a magnetic source (2) configurable for applying an external magnetic flux (Φ) through the superconducting loop; the flux quantum bit (QB) having a first and a second energy well separated by an energy barrier; the height of the energy barrier being configurable by the modulation of the critical current (Ic) of said Josephson effect quantum component (10) by the control means (CONT).
  13. 13. Quantum flux bit (QB) according to the preceding claim wherein said magnetic source (2) is configured to modulate the phase induced by the external magnetic flux (Φ) so as to control the position of the energy barrier relative to the second energy well.
  14. 14. Quantum memory (QM) for storing quantum data comprising: - a superconducting loop formed by two quantum devices (1, 1') according to any one of the preceding claims electrically mounted in parallel and arranged symmetrically in the superconducting loop; the first quantum device (1) being configured at a first predetermined critical current value (Ic1) and the second quantum device (1') being configured at a second predetermined critical current value (Ic2); the value of the quantum data being encoded by the difference between the first critical current value (Ic1) and the second critical current value (Ic2).
  15. 15. Quantum memory (MQ) according to claim 14 further comprising reading means (LECT) configured to apply a reading current (I_lect) in the superconducting loop having an amplitude less than or equal to one hundredth of the writing current (I_wr).

Description

DESCRIPTION Title of the invention: Modulable quantum device with Josephson effect Scope of application [0001] The present invention relates to the field of quantum devices comprising one or more Josephson junctions. More particularly, the invention relates to a flux qubit and a multilevel quantum memory based on Josephson junctions having adjustable characteristics. Problem raised [0002] Josephson junctions comprising superconducting materials are used in the design of several types of quantum devices. Superconductivity is the particularity, for certain materials called superconductors, of having zero electrical resistance when their temperature is below a temperature called the critical temperature. Superconductivity is caused by the phenomenon of formation of Cooper pairs consisting of two coupled electrons. [0003] A Josephson junction is formed by two layers of superconductors separated by a non-superconducting barrier layer. The barrier is thin enough for the Cooper pairs to be able to pass through it. The Cooper pairs can then migrate from one superconducting layer to another, by tunneling if the barrier layer is a dielectric or by electrical conduction if the barrier layer is an ohmic conductor. Indeed, the wave function of the Cooper pairs of the first superconductor interferes with the wave function of the Cooper pairs of the second superconductor through the barrier layer. This induces a passage of electric current through the junction despite the material discontinuity of the structure. [0004] More particularly, the flux quantum bit solutions currently used in quantum computers require the implementation of several additional complex compensation circuits to permanently bias the flux quantum bit. The bias is necessary to compensate for drifts resulting from manufacturing defects. The circuits are also necessary to perform logic operations from the quantum bits. The same constraints are encountered for the production of cryogenic memories intended to be used in RSFQ (Rapid Single Flux Quantum) type computers. Indeed, in known solutions, complex structures with control lines and SQUID (Superconducting QUantum Interference Device) magnetometer structures nested inside another SQUID are used. This type of architecture is particularly complex for manufacturing but also for the spatial implementation of the architecture. [0005] In addition, known flux quantum bit structures do not allow the superconducting current flowing in the superconducting loop of the qubit and the energy of the tunnel effect to be controlled independently at the same time. This leads to the use of complex architectures based on the assembly of several SQUID type magnetometers where the adjustment is carried out using external magnetic fields. [0006] Moreover, known SQUID-based flux qubits exhibit a high sensitivity to variabilities due to manufacturing asymmetries, particularly in Josephson junctions. This leads to a loss of precision in the execution of quantum computing algorithms. Indeed, to obtain reliable execution of adiabatic quantum computing algorithms (AQO for Adiabatic Quantum Optimization), mastery of the following two parameters is essential: - The superconducting current through the Josephson quantum devices; - The energy of the tunnel effect through the Josephson quantum devices; [0007] A technical problem to be solved in this context therefore consists in designing a Josephson quantum device making it possible to produce flux quantum bits and/or multilevel quantum memories without resorting to complex circuitry for compensating for the effects of technological variabilities. Prior Art/State of the Art Restrictions [0008] US patent US10546621B2 describes a quantum memory structure compatible with superconducting logic gates. The described solution is based on a SQUID nested inside another SQUID. The disadvantage of the solution described by this document is that it is limited only to materials with a low critical temperature Tc. In addition, the operations of reading/writing quantum data in this type of memory require a plurality of current lines. This increases the complexity of implementing the structure and increases its energy consumption. Response to the problem and provision of a solution [0009] To overcome the limitations of existing solutions with regard to the control of the parameters of Josephson effect structures in quantum computing devices, the invention proposes several embodiments of a quantum device comprising a Josephson effect component having a modulatable critical current and control means. In the quantum component according to the invention, the junction structure between the two superconducting layers comprises a ferromagnetic layer with a heterogeneous magnetic domain. The volume distribution of the domains in the volume of said ferromagnetic layer is modulatable via the application of a write current generated by the control means. The modification of the volume distribution of the magnet