Modular quantum device with Josephson effect

Abstract

The invention relates to a quantum device comprising: a Josephson effect quantum component having a tunable critical current, fabricated on a first face of a substrate, and comprising: a first layer of a first superconducting material, a second layer of a second superconducting material; a junction structure connecting the first layer to the second layer and comprising a heterogeneous domain ferromagnetic layer having at least a first magnetic domain along a first direction and a second magnetic domain along a second direction opposite to the first direction; control means configured to apply a writing current through the heterogeneous domain ferromagnetic layer to modify the volume distribution of the two magnetic domains in said heterogeneous domain ferromagnetic layer in order to modulate said critical current. Figure for the abstract: Fig. 1

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 multi-level 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 characteristic, 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 the 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 Cooper pairs to pass through it. Cooper pairs can then migrate from one superconducting layer to the other, 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 specifically, 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 for use in RSFQ (Rapid Single Flux Quantum) type computers. Indeed, in the 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] Furthermore, known flux quantum bit structures do not allow independent control of the superconducting current flowing in the superconducting loop of the qubit and the tunneling energy at the same time. This requires 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 variability 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 the English expression Adiabatic Quantum Optimization), control of the following two parameters is essential: - The superconducting current through the Josephson effect quantum devices; - the energy of the tunnel effect through Josephson quantum devices;

[0007] A technical problem to be solved in this context therefore consists of designing a Josephson effect quantum device making it possible to produce flux quantum bits and / or multi-level quantum memories without resorting to complex circuitry for compensating for the effects of technological variability. Prior Art / State of the Art Restrictions

[0008] US patent US10546621B2 describes a quantum memory structure compatible with superconducting logic gates. The solution described 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 Te. In addition, the read / write operations of quantum data in this type of memory require a plurality of current lines. This increases the implementation complexity of 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 ferroma layer heterogeneous magnetic domain magnetic field. The volume distribution of the domains in the volume of said ferromagnetic layer can be modulated via the application of a write current generated by the control means. The modification of the volume distribution of the magnetic domains makes it possible to control the critical current of the Josephson junction and thus control the superconducting current through the quantum devices.

[0010] Furthermore, the invention provides a quantum bit comprising a superconducting loop with a modulatable Josephson junction according to the invention. This makes it possible to compensate for the effects of variabilities and asymmetries between the quantum bits constituting a quantum computer by controlling the parameters of each quantum bit independently.

[0011] Furthermore, the invention proposes a quantum memory for storing quantum data comprising a superconducting loop formed by two modulatable Josephson junctions according to the invention. Each Josephson junction of the loop is programmed so as to obtain two distinct critical currents. This asymmetry makes it possible to store quantum data coded by the difference between the first critical current value and the second critical current value. This solution makes it possible to produce a quantum memory with a simple implementation, thus reducing the hardware complexity of the calculation circuit. Summary / Claims

[0012] The subject of the invention is a quantum device comprising: - a Josephson effect quantum component having a modulatable critical current, produced on a first face of a substrate, and comprising: • a first layer of a first superconducting material, • a second layer of a second superconducting material; • a junction structure connecting the first layer to the second layer and comprising a ferromagnetic layer with a heterogeneous domain having at least a first magnetic domain in a first direction and a second magnetic domain in a second direction opposite to the first direction; - control means configured to apply a write current through the heterogeneous domain ferromagnetic layer to modify the volume distribution of the two magnetic domains in said heterogeneous domain ferromagnetic layer in order to modulate said critical current.

[0013] According to a particular aspect of the invention, the thickness of the ferromagnetic layer with heterogeneous domain is less than or equal to 10 nm.

[0014] According to a particular aspect of the invention, the thickness of the first layer and / or the second layer is between 20nm and 500nm.

[0015] According to a particular aspect of the invention, the ferromagnetic layer with heterogeneous domain forms a band having a non-zero curvature; said band extending along a plane parallel to the first face of the substrate.

[0016] According to a particular aspect of the invention, the ferromagnetic layer with heterogeneous domain forms a U-shaped or semi-circular or sinusoidal band; said band extending along a plane parallel to the first face of the substrate.

[0017] According to a particular aspect of the invention, the junction structure is confined between, on the one hand, the first layer deposited on the first face of a substrate and, on the other hand, the second layer.

[0018] According to a particular aspect of the invention, the first layer and the second layer are coplanar; the junction structure resting on at least a part of the first layer and on at least a part of the second layer.

[0019] According to a particular aspect of the invention, the junction structure further comprises a ferromagnetic layer with a fixed homogeneous domain arranged between the first layer and the ferromagnetic layer with a heterogeneous domain.

[0020] According to a particular aspect of the invention, the junction structure further comprises a magnetic decoupling layer confined between the ferromagnetic layer with fixed homogeneous domain and the ferromagnetic layer with heterogeneous domain.

[0021] According to a particular aspect of the invention, the thickness of the ferromagnetic layer with fixed homogeneous domain is greater than twice that of the ferromagnetic layer with heterogeneous domain.

[0022] According to a particular aspect of the invention, the ferromagnetic layer with heterogeneous domain is made of Ni or NiFe or NiCo or CoFeBo or CoPt or LSMO or LCMO.

[0023] The invention also relates to a flux quantum bit comprising: - a superconducting loop formed by the quantum device according to the invention; - a configurable magnetic source to apply an external magnetic flux through the superconducting loop; the flux quantum bit 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 of said Josephson effect quantum component by the control means.

[0024] According to a particular aspect of the invention, said magnetic source is configured to modulate the phase induced by the external magnetic flux so as to control the position of the energy barrier relative to the second energy well.

[0025] The invention also relates to a quantum memory for storing quantum data comprising: - a superconducting loop formed by two quantum devices according to the invention electrically mounted in parallel and arranged symmetrically in the superconducting loop; the first quantum device being configured at a first predetermined critical current value and the second quantum device being configured at a second predetermined critical current value; the value of the quantum data being encoded by the difference between the first critical current value and the second critical current value.

[0026] According to a particular aspect of the invention, the quantum memory further comprises reading means configured to apply a reading current in the superconducting loop having an amplitude less than or equal to one hundredth of the writing current. Detailed Description

[0027] Other characteristics and advantages of the present invention will appear better on reading the description which follows in relation to the following appended drawings.

[0028] [Fig-1] [Fig.l] illustrates a sectional view of a quantum device according to a first embodiment of the invention.

[0029] [Fig.2a] [Fig.2a] illustrates a top view of a first example of the iron layer heterogeneous domain romagnetic used in the quantum device according to the invention.

[0030] [Fig.2b] [Fig.2b] illustrates a top view of a second example of the iron layer heterogeneous domain romagnetic used in the quantum device according to the invention.

[0031] [Fig.3] [Fig.3] illustrates the variation of the critical current of the quantum component according to the first embodiment of the invention depending on the volume distribution of the magnetic domains in the ferromagnetic layer.

[0032] [Fig.4] [Fig.4] illustrates a sectional view of a quantum device according to a second embodiment of the invention.

[0033] [Fig.5] [Fig.5] illustrates a sectional view of a quantum device according to a third embodiment of the invention.

[0034] [Fig.6] [Fig.6] illustrates the variation of the critical current of the quantum component according to the third embodiment of the invention as a function of the volume distribution of the magnetic domains in the ferromagnetic layer.

[0035] [Fig.7] [Fig.7] illustrates a sectional view of a quantum device according to a fourth embodiment of the invention.

[0036] [Fig.8a] [Fig.8a] illustrates an electrical modeling of a quantum bit according to the invention.

[0037] [Fig.8b] [Fig.8b] illustrates a structural representation in top view of a quantum bit according to the invention

[0038] [Fig.8c] [Fig.8c] illustrates the potential diagram of the quantum bit according to the invention.

[0039] [Fig.9a] [Fig.9a] illustrates a top view of a quantum memory according to the invention.

[0040] [Fig.9b] [Fig.9b] illustrates the electrical response of a quantum memory according to the invention compared to a symmetrical superconducting loop.

[0041] [Fig.l] illustrates a sectional view of a quantum device 1 according to a first embodiment of the invention. The quantum device 1 comprises a substrate SUB, a Josephson effect quantum component 10 produced on a first face of the substrate SUB and control means, not shown.

[0042] The Josephson effect quantum component 10 is a Josephson junction having a modulatable critical current 11. The critical current 11 of a Josephson junction is the maximum current beyond which the quantum component does not operate in a superconducting regime. The Josephson effect quantum component 10 comprises a first layer 11 made of a superconducting material, a second layer 12 made of a superconducting material and a junction structure 20 connecting the first layer 11 to the second layer 12.

[0043] The substrate SUB is the mechanical support of the quantum component 10. The substrate SUB is made of Silicon Si or Sapphire A12O3 or magnesium oxide MgO or lanthanum aluminate LAO, among others. Advantageously, the substrate SUB comprises a buffer layer 16 deposited on the first face of said substrate. The buffer layer is made of cerium oxide CeO2 or zirconia stabilized with yttrium oxide YSZ. The buffer layer 16 makes it possible to achieve a lattice agreement with the first layer 11 to facilitate the epitaxial growth of said first layer 11.

[0044] The first layer 11 is made of Nb or NbSn or Al or AIN or MoSi or YBCO or NdBCO or LaBCO or BCCO, among others. The first layer 11 has a thickness typically between 20 nm and 500 nm.

[0045] The second layer 12 is deposited on the junction structure 20. The second layer 12 is made of Nb or NbSn or Al or AIN or MoSi or YBCO or NdBCO or LaBCO or BCCO. The second layer 12 has a thickness of between 20nm and 500nm.

[0046] The junction structure 20 comprises a heterogeneous domain ferromagnetic layer 13. The ferromagnetic layer 13 is confined between the first layer 11 and the second layer 12. The ferromagnetic layer 13 has a first magnetic domain DI in a first direction and a second magnetic domain D2 in a second direction opposite to the first direction. For example, the first domain DI is composed of magnetic moments directed upwards, the second domain D2 is composed of magnetic moments directed downwards. The heterogeneous domain ferromagnetic layer 13 plays the role of the non-superconducting barrier in the Josephson junction. The thickness of the heterogeneous domain ferromagnetic layer 13 is less than or equal to 10 nm. The heterogeneous domain ferromagnetic layer 13 is made of Ni or NiFe or NiCo or CoFeBo or CoPt or LSMO or LCMO.

[0047] According to the plane (X,Y) parallel to the first face of the substrate SUB, the ferromagnetic layer with heterogeneous domain 13 forms a strip having a non-zero curvature according to a plane parallel to the first face of the substrate SUB. By way of example, the ferromagnetic layer 13 forms a U-shaped (more particularly horseshoe-shaped) or semi-circular or sinusoidal strip according to the plane (X,Y) as illustrated in FIGS. 2a and 2b. [Fig.2a] illustrates a top view of a first example of the ferromagnetic layer 13 with two distinct magnetic domains. [Fig.2b] illustrates a top view of a second example of the ferromagnetic layer 13 with several series of magnetic domains with opposite directions.

[0048] The combination of the curved strip shape and the small thickness make it possible to obtain the heterogeneous magnetic distribution of domains with the appearance of a separation barrier between the domains. The volume of the area occupied by the separation barrier between the domains is ten times smaller than the total volume of the heterogeneous domain ferromagnetic layer 13. The width of the separation barrier between the domains is between 50nm and 300nm. The non-rectilinear shape of the ferromagnetic layer 13 can be achieved by etching and lithography techniques compatible with the materials used.

[0049] The stacking of layers is achieved by deposition techniques such as cathode sputtering, pulsed laser ablation, or evaporation deposition. The non-rectilinear shape of the ferromagnetic layer 13 is achieved by electron beam etching techniques or ion beam etching.

[0050] In the Josephson effect quantum component 10 according to the invention, the critical current Ic depends on the volume distribution of the magnetic magnetization domains in the volume of the ferromagnetic layer 13, acting as a barrier in the junction. By way of illustration, [Fig.2a] shows a ferromagnetic layer 13 with half of its volume occupied by DI and the other half occupied by a domain D2. We thus speak of a magnetic distribution with a volume occupied 50% by the first domain DI (magnetization upwards) and 50% by the second domain D2 (magnetization downwards). The volume distribution of the magnetic magnetization domains can be modulated by injecting a write current Iwr at across the junction. The electrons of the current injected from the first layer 11 to the second layer 12 (or vice versa) through the junction structure 20 apply a moment to the electrons of the atoms constituting the ferromagnetic layer 13. It is thus possible to modify the volume distribution of the magnetic magnetization domains in the volume of the ferromagnetic layer 13 according to the direction and intensity of the writing current Iwr.

[0051] The quantum device 1 comprises control means configured to apply said write current Iwr through the heterogeneous domain ferromagnetic layer 13 to modify the volume distribution of the magnetic domains in order to modulate said critical current Ic according to a set value. Alternatively, the volume distribution of the domains is modulated by the application of a magnetic field.

[0052] [Fig.3] illustrates the variation of the critical current Ic of the quantum component 10 according to the first embodiment of the invention as a function of the volume distribution of the magnetic domains in the ferromagnetic layer 13.

[0053] Consider a first distribution configuration with a volume occupied 50% by the first domain DI (magnetization upwards) and 50% by the second domain D2 (magnetization downwards). When the control means configure the ferromagnetic layer 13 according to the first configuration, the critical current Ic of the Josephson effect quantum component 10 is at a minimum value ICi. This corresponds to a high resistive state of the quantum component 10. Consider a second distribution configuration with a volume occupied 100% by the first domain DI (magnetization upwards) and 0% by the second domain D2 (magnetization downwards).When the control means configure the ferromagnetic layer 13 according to the second configuration, the critical current Ic of the Josephson effect quantum component 10 is at a maximum value IC2- The value of the critical current Ic evolves continuously between the first configuration (50% Dl-50% D2) and the second configuration (100% Dl-0%D2). Thus, the control means are able to modulate the value of the critical current Ic (and therefore the resistivity of the quantum component) using the write current Iwr*.

[0054] Consider a third distribution configuration with a volume occupied at 0% by the first domain DI (magnetization upwards) and at 100% by the second domain D2 (magnetization downwards). When the control means configure the ferromagnetic layer 13 according to the third configuration, the critical current Ic of the Josephson effect quantum component 10 is at a maximum value IC2- The value of the critical current Ic evolves in a continuous manner between the first configuration (50% Dl-50% D2) and the third configuration (0% Dl-100% D2). Thus, in an alternative manner, it is possible to control the critical current Ic of the quantum component 10 between the two aforementioned configurations using the write current Iwr.

[0055] The quantum device 1 according to the invention constitutes a Josephson junction with a critical current that can be continuously modulated using the distribution control of the magnetic domains of the heterogeneous domain ferromagnetic layer 13. This degree of freedom of control makes it possible to compensate for the effects of variability and asymmetry for the implementation of a reliable quantum system (quantum processor for example).

[0056] [Fig.4] illustrates a sectional view of a quantum device 1 according to a second embodiment of the invention. The second embodiment differs from the first embodiment by the arrangement of the layers constituting the Josephson effect quantum component 10. The first superconducting layer 11 and the second superconducting layer 12 are coplanar. The two superconducting layers 11, 12 are both deposited on the first face of the substrate SUB. The two superconducting layers 11, 12 are separated in the same plane by a dielectric volume having a width greater than 10 nm, for example. The junction structure 20 consists of the heterogeneous domain ferromagnetic layer 13 similar to the first embodiment. The heterogeneous domain ferromagnetic layer 13 rests on one side on a part of the upper surface of the first superconducting layer 11.The heterogeneous domain ferromagnetic layer 13 rests on the other side on a part of the upper surface of the second superconducting layer 12. During operation under a superconducting regime, the application of a potential difference between the superconducting layers 11, 12 induces a Cooper pair current I through the junction structure 20.

[0057] In this embodiment, the curve of evolution of the critical current Ic as a function of the distribution of the magnetic domains D1, D2 is similar to that described for the first embodiment.

[0058] The coplanarity of the superconducting layers 11, 12 makes it possible to simplify the manufacturing process of the quantum device 1. In fact, a single epitaxial growth operation is necessary to manufacture the two superconducting layers instead of two epitaxial operations to produce the stack according to the first embodiment.

[0059] [Fig. 5] illustrates a sectional view of a quantum device 1 according to a third embodiment of the invention. The third embodiment differs from the first embodiment by the composition of the junction structure 20 confined between the first superconducting layer 11 and the second superconducting layer 12. Indeed, the junction structure 20 further comprises a ferromagnetic layer with a fixed homogeneous domain 14 and a magnetic decoupling layer 15. The ferromagnetic layer with a fixed homogeneous domain 14 is deposited on the first superconducting layer 12. conductive 11. The magnetic decoupling layer 15 is confined between the fixed homogeneous domain ferromagnetic layer 14 and the heterogeneous domain ferromagnetic layer 13. The fixed homogeneous domain ferromagnetic layer 14 has a single fixed magnetization direction in its volume. The homogeneous ferromagnetic layer 14 has a thickness greater than twice that of the heterogeneous ferromagnetic layer 13. The magnetic decoupling layer 15 makes it possible to magnetically decouple the heterogeneous domain ferromagnetic layer 13 from the homogeneous domain ferromagnetic layer 14. For example, the magnetic decoupling layer 15 is made of Cu, Al, MgO or A12O3. The magnetic decoupling layer 15 has a thickness between 1 nm and 10 nm so that the two ferromagnetic layers 13 and 14 are decoupled while allowing spin transport across the interface which separates them.

[0060] Following the application of a readout voltage, the Cooper pairs originating from the first superconducting layer 11 interact with the fixed magnetic moment of the homogeneous domain ferromagnetic layer 14. This interaction induces a change in the direction of the spin of the Cooper pairs passing through the homogeneous ferromagnetic layer 14 towards the heterogeneous ferromagnetic layer 13. The spin of the electrons passing through the homogeneous ferromagnetic layer 14 aligns with the direction of said layer 14. Then, at the interface with the heterogeneous ferromagnetic layer 13, the penetration of electrons having a magnetization aligned with that of the encountered domain is favored. Conversely, when the electron has a magnetization opposite to that of the encountered domain at the interface with the heterogeneous ferromagnetic layer 13, the transmission rate of the Cooper pairs is reduced.Thus, it is possible to modulate the critical current Ic of the junction structure 20 by controlling the volume distribution of the magnetization domains in the heterogeneous ferromagnetic layer 13 relative to the fixed magnetization direction of the homogeneous ferromagnetic layer 14.

[0061] [Fig.6] illustrates the variation of the critical current Ic of the quantum component 10 according to the third embodiment of the invention as a function of the volume distribution of the magnetic domains in the heterogeneous ferromagnetic layer 13. In the example illustrated, the magnetization in the fixed homogeneous ferromagnetic layer 14 is directed along D2.

[0062] Similar to the embodiment of [Fig.3], when the control means configure the ferromagnetic layer 13 according to the first configuration (100% Dl, 0% D2), the critical current Ic of the Josephson effect quantum component 10 is at a minimum value Here.

[0063] When the control means configure the ferromagnetic layer 13 according to the third configuration (0% Dl, 100% D2), the critical current Ic of the component Josephson effect quantum field 10 is at a maximum value IC2- This corresponds to a magnetization alignment between the electrons and the magnetization of the ferromagnetic layer 13. This induces a minimum resistivity of the junction structure 20.

[0064] Conversely, when the control means configure the ferromagnetic layer 13 according to the third configuration (100% D1, 0% D2), the critical current 1c of the Josephson effect quantum component 10 is at a minimum value Here. This corresponds to an opposition of the magnetization direction between the electrons and the magnetization of the ferromagnetic layer 13. This induces a maximum resistivity of the junction structure 20.

[0065] The value of the critical current Ic evolves continuously between the first configuration (50% Dl-50% D2) and the third configuration (0% Dl-100% D2). The value of the critical current Ic evolves along an asymptotic straight line between the first configuration (50% Dl-50% D2) and the second configuration (100% Dl-0% D2). Thus, the control means of the invention are capable of modulating the value of the critical current Ic (and therefore the resistivity of the quantum component) using the write current Iwr. The embodiment makes it possible to cover a wider range of domain distribution than that of the first embodiment. This results in a more flexible control advantage.

[0066] [Fig. 7] illustrates a sectional view of a quantum device 1 according to a fourth embodiment of the invention. The fourth embodiment differs from the third embodiment by the arrangement of the layers constituting the Josephson effect quantum component 10. The first superconducting layer 11 and the second superconducting layer 12 are coplanar. The two superconducting layers 11, 12 are both deposited on the first face of the substrate SUB. The two superconducting layers 11, 12 are separated in the same plane by a dielectric volume having a width greater than 10 nm. The heterogeneous domain ferromagnetic layer 13 rests on the second superconducting layer 12. The magnetic decoupling layer 15 consists of a first part deposited on the separation dielectric and a second part deposited on the heterogeneous domain ferromagnetic layer 13.The fixed homogeneous domain ferromagnetic layer 14 comprises a first part deposited on the first superconducting layer 11 and a second part deposited on the magnetic decoupling layer 15.

[0067] In this embodiment, the evolution curve of the critical current Icen as a function of the distribution of the magnetic domains D1, D2 is similar to that described for the third embodiment.

[0068] The coplanarity of the superconducting layers 11, 12 makes it possible to simplify the manufacturing process of the quantum device 1. In fact, a single epitaxial growth operation is necessary to manufacture the two superconducting layers instead of two epitaxy operations to achieve the stacking according to the third embodiment.

[0069] Figure 8a illustrates an electrical modeling of a quantum bit QB according to the invention. Figure 8b illustrates a structural representation in top view of a quantum bit QB according to the invention. The quantum bit QB comprises a supra-loop conductive formed by the quantum device 1 and a magnetic source 2 configurable to apply an external magnetic flux 9? through the supra-loop conductive. The quantum bit QB is equivalent to a circuit having an inductance L.

[0070] The Hamiltonian of this device is - / ?COS <p with Uc the capacitive energy of the Josephson quantum component 10, Uj the Josephson energy proportional to the inductance L, q> the phase difference across the junction structure 20 and <px la phase induite par la présence du flux magnétique externe ¢. Le paramètre / 5 s’exprime selon l’équation suivante « = , with the critical current of the quantum device 1, and <e>0 the quantum of flux.

[0071] Figure 8c illustrates the potential diagram of the QB quantum bit according to q> the phase difference across the junction structure 20. The energy diagram associated with the QB flux quantum bit has a first energy well and a second energy well. The first energy well corresponds to a first energy state EL. The second energy well corresponds to a second energy state E2. The two energy states El and E2 are separated by an energy barrier BW. The energy barrier BW is defined by its height and by its position relative to the two minima of the energy wells El, E2. The energy barrier is located at a phase shift<p=ir. Une parabole de fond est définie avec un centrage à q> = <px. Les positions des deux minimum des puits d’énergie El, E2 dépendent du déphasage <px- jt. La hauteur de la barrière d’énergie BW est proportionnelle à / ).Thus, the energy barrier BW can be controlled completely independently and continuously in position and height. The height is modified by modulating the critical current Ic of the quantum device 1. The position of the barrier relative to the second energy well is modifiable by changing the external magnetic flux ¢. This independent control is necessary for the implementation of the algorithms used in adiabatic quantum optimization processors. In addition, this makes it possible to compensate for the effects of variabilities and asymmetries between the quantum bits constituting a quantum computer by controlling the parameters of each quantum bit independently in order to homogenize them.

[0072] [Fig.9a] illustrates a top view of a quantum memory MQ according to the invention. Quantum memory MQ is a cryogenic multi-level memory. The quantum memory MQ comprises a superconducting loop formed by two quantum devices 1 and 1' according to the invention. The two quantum devices 1 and 1' are electrically connected in parallel. The two quantum devices 1 and 1' are arranged symmetrically in the superconducting loop. The first quantum device 1 is configured at a first predetermined critical current value ICi. The second quantum device 1' is configured at a second predetermined critical current value IC2. In the example illustrated, the first critical current ICi is greater than the second critical current IC2 - H is then an asymmetric loop from a resistivity point of view.

[0073] This asymmetry makes it possible to encode the value of a quantum data item by the difference between the first critical current value ICi and the second critical current value IC2*. Indeed, when a read current Iiect is injected into the loop, the current Ii which flows in the first branch comprising the first quantum device 1 is greater than the current I2 in the first branch comprising the first quantum device 1'. This current difference induces the creation of a magnetic flux Ad) through the loop. The magnetic flux AO induces the appearance of a non-zero electrical voltage VI at the terminals of the loop. The amplitude of the non-zero electrical voltage VI is proportional to the difference in critical currents ICr Ic2- Thus, by modulating the critical currents ICi and IC2 via the control means, it is possible to write and store a quantum data item in the quantum memory MQ according to the invention.

[0074] In order to understand the effect of asymmetry, Figure 9b illustrates the electrical response C i of an asymmetric quantum memory MQ compared to the electrical response Co of a symmetric quantum memory MQ. The curves Ci and Co present the electrical voltage at the terminals of the loop as a function of an external magnetic flux ¢. In both cases, it is a sinusoidal variation as a function of the magnetic flux ¢. The curve Co (symmetric loop) is centered on the ordinate axis: at 0 = 0, the voltage V is zero. The curve Ci (asymmetric loop ICi > Ici) is shifted to the left relative to the curve Co. The shift is equal to the phase shift induced by the asymmetry. Thus, for d? = 0, a non-zero electrical voltage VI is measured at the terminals of the loop. The amplitude of the measured voltage VI depends on the reaction magnetic flux Ad> and therefore on the critical current difference ICi-Ic2-

[0075] The quantum memory MQ comprises reading means LECT for generating the reading current Iiect. The reading current Iiect has an amplitude less than or equal to one hundredth of the writing current Iwr generated by the control means. This makes it possible to present the stored quantum data during reading.< / e>

Claims

Claims

1. Quantum device (1) comprising: - a Josephson effect quantum component (10) having a modulatable critical current (Ie), produced on a first face of a substrate (SUB), and comprising: • a first layer (11) made of a first superconductor material, • a second layer (12) made of a second superconductor material; • a junction structure (20) connecting the first layer (11) to the second layer (12) and comprising a ferromagnetic layer with a heterogeneous domain (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 write 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. A 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. 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. Quantum device (1) according to any one of claims 1 to 3 in which the heterogeneous domain ferromagnetic layer (13) forms a band having a non-zero curvature; said band extending along a plane (X,Y) parallel to the first face of the substrate (SUB).

5. Quantum device (1) according to claim 4 wherein the heterogeneous domain ferromagnetic layer (13) forms a U-shaped or semi-circular or sinusoidal band; said band extending along a plane (X,Y) parallel to the first face of the substrate (SUB).

6. Quantum device (1) according to any one of claims 1 to 5 wherein 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. 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. A 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 (Cl) and the heterogeneous domain ferromagnetic layer (13).

9. The quantum device (1) of 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. A 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. A quantum device (1) according to any preceding claim wherein the heterogeneous domain ferromagnetic layer (13) is made of Ni or NiFe or NiCo or CoFeBo or CoPt or LSMO or LCMO.

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 to apply an external magnetic flux (¢) 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 (le) said Josephson effect quantum component (10) by the control means (CONT).

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 (0) so as to control the position of the energy barrier relative to the second energy well.

14. Quantum memory (MQ) 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 (Ici) 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 (Ici) and the second critical current value (Ic2).

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).

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