Room temperature operable spin qubit and quantum entanglement structure using spin qubit

Abstract

A spin qubit operable at room temperature by using a magnetic tunnel junction is disclosed. The spin qubit consists of two MTJs, and the magnetization of a free layer is determined by an overlapping wire crossing the MTJs or by an underlying nonmagnetic heavy metal layer. Compared to fixed layers having perpendicular magnetic anisotropy according to a formed external magnetic field, the free layer may implement a superposition state. In addition, quantum entanglement is implemented by disposing an entanglement wire between spin qubits.

Description

Room-temperature operating spin qubits and quantum entanglement structures using spin qubits

[0001] The present invention relates to a qubit used in quantum computing, and more particularly, to a spin qubit operating at room temperature through spin direction control of a free layer in a complementary structure composed of two magnetic tunnel junction structures, and a quantum entanglement structure using a spin qubit.

[0002] A quantum computer is defined as a computing device that operates using quantum principles. Quantum principles refer to superposition, entanglement, and coherence, and qubits, based on the laws of quantum mechanics, are used as unit elements.

[0003] Superposition refers to the phenomenon where a particle exists in multiple states prior to observation, and is resolved into a single state at the moment of observation. For example, an electron exists in a superposition of multiple states prior to observation, which is expressed as a probabilistic wave function. Furthermore, upon observation, the electron is resolved into a single position, and thereafter behaves like a particle. In a quantum superposition state, a quantum system exists in multiple states simultaneously, much like a wave, and is resolved into a single state at the moment of measurement.

[0004] Entanglement is described as a state in which two quantum systems are intimately linked, whereby information about one provides instantaneous information about the other, regardless of physical distance. This refers to a state in which measuring one particle can instantly yield conclusions or information about the other. For example, if one qubit rotates upward, the other qubit can always be determined to be rotating downward. This provides the foundation for quantum computers to rapidly solve complex problems.

[0005] Coherence refers to the phenomenon in a quantum system where two or more quantum states interact while maintaining a phase relationship. This is a crucial characteristic of quantum computing, and while coherence is maintained, quantum systems can effectively utilize superposition and entanglement states. Due to the phase relationship between quantum states, two quantum states maintain a constant phase difference, resulting in interference between them.

[0006] In particular, quantum coherence is closely related to superposition states. Quantum states in a coherent state exhibit interference phenomena, allowing operations to be performed through quantum gates.

[0007] As mentioned above, the smallest computational unit in quantum computing is the qubit. This is a bit to which the principles of quantum mechanics apply, and thanks to the principle of superposition, a single qubit has the advantage of being able to express multiple states simultaneously.

[0008] Figure 1 is a perspective view for explaining the operation of qubits using a superconducting Josephson junction according to the prior art.

[0009] Referring to FIG. 1, two superconducting qubits (10, 20) are arranged, and a connection circuit (30) is provided between the superconducting qubits (10, 20).

[0010] Qubits (10, 20) and connection circuits (30) are composed of superconductors. In addition, control lines (40) are connected to the qubits (10, 20) and control the operation of the qubits (10, 20).

[0011] The connection circuit (30) implements a quantum entanglement state of two qubits (10, 20). In the quantum entanglement state, information of the second qubit (20) is determined based on information of the first qubit (10). In addition, when the quantum entanglement state is released, the first qubit (10) or the second qubit (20) can each implement a superposition state.

[0012] Qubits (10, 20) and a connection circuit (30) have a Josephson junction. The Josephson junction includes a thin oxide film interposed between superconductors. In the Josephson junction, the two superconductors are separated from each other, have independent phases, and Cooper pairs can quantum tunnel to move to the other superconductor.

[0013] The operation of the connection circuit (30) and qubits (10, 20) is controlled by applying microwaves.

[0014] A state in which no microwave is applied to the connection circuit (30) is a state in which quantum entanglement does not occur, and when a microwave is applied only to the first qubit (10), the direction of the superconducting current in the structure including the Josephson junction changes. Therefore, the direction of the superconducting current of the first qubit (10) can be changed. For example, it is assumed that the direction of the superconducting current of the first qubit (10) initially has a clockwise direction (↑, assumed in the up direction). By applying an appropriate microwave, the direction of the superconducting current of the first qubit (10) is not determined as clockwise or counterclockwise. This is a superposition state (assumed in the direction of → or ←), and when another additional microwave is applied, the direction of the superconducting current of the first qubit (10) changes to a counterclockwise direction (↓, assumed in the down direction). That is, by applying a microwave to one qubit, the direction of the superconducting current can be implemented in a clockwise, counterclockwise, and superposition state.

[0015] When a microwave is applied to the connection circuit (30), quantum entanglement is realized. It is assumed that before the microwave is applied, the superconducting current direction of the first qubit (10) is clockwise (↑) and the superconducting current direction of the second qubit (20) is counterclockwise (↓). When the microwave is applied only to the connection circuit (30), the superconducting current direction of the first qubit (10) is counterclockwise (↓), and the spin of the second qubit (20) changes to a clockwise (↑) superconducting current direction.

[0016] If we set ↓ to 0 and spin ↑ to 1 according to the direction of superconducting current flow, the superposition state → or ← becomes a state where 0 and 1 coexist, and when this is observed from the outside, 0 and 1 appear as probabilities. In other words, 0 and 1 coexist in one qubit, and 0 and 1 can be expressed simultaneously as a probability function.

[0017] Moreover, in a quantum entangled state, this is extended so that in a 2-bit qubit structure, four states can be derived as probability functions simultaneously.

[0018] Quantum computing is performed based on the above principles. However, the technology shown in Figure 1 has certain limitations. Specifically, it requires a superconductor and must operate in an ultra-low-temperature environment. Furthermore, it has the limitation of requiring microwaves, a type of electromagnetic wave, to be applied to each qubit.

[0019] The first technical task to be achieved by the present invention is to provide a spin qubit that utilizes a magnetic tunnel junction structure and operates at room temperature.

[0020] In addition, the second technical task to be achieved by the present invention is to provide a quantum entanglement structure using a spin qubit provided by achieving the first technical task.

[0021] In order to achieve the first technical problem described above, the present invention provides a spin qubit, comprising: a first MTJ having a first free layer, a first tunnel junction layer formed on the first free layer, and a first pinned layer formed on the first tunnel junction layer; a second MTJ having a second free layer, a second tunnel junction layer formed on the second free layer, and a second pinned layer formed on the second tunnel junction layer; and an overlapping wiring disposed between the first MTJ and the second MTJ, the overlapping wiring having a first overlapping wiring adjacent to the first MTJ and a second overlapping wiring adjacent to the second MTJ, wherein directions of current flowing through the first overlapping wiring and the second overlapping wiring are opposite to each other, the first MTJ and the second MTJ are connected in parallel with each other, magnetization directions of the first pinned layer and the second pinned layer are opposite to each other, and the overlapping wiring is characterized in that it extends in a direction perpendicular to an imaginary plane connecting growth directions of the first MTJ and the second MTJ.

[0022] The first technical problem of the present invention can also be achieved by providing a spin qubit including a first MTJ having a first free layer, a first tunnel junction layer formed on the first free layer, and a first pinned layer formed on the first tunnel junction layer; a second MTJ having a second free layer, a second tunnel junction layer formed on the second free layer, and a second pinned layer formed on the second tunnel junction layer; and a non-magnetic heavy metal layer that is commonly connected to lower portions of the first free layer and the second free layer to induce a spin-orbit torque in the first free layer and the second free layer to control the magnetization states of the first free layer and the second free layer, wherein the first MTJ and the second MTJ are connected in parallel with each other, and the magnetization directions of the first pinned layer and the second pinned layer are opposite to each other.

[0023] The present invention for achieving the second technical task provides a quantum entanglement structure of a spin qubit, comprising: a first spin qubit composed of two parallel-connected MTJs; a second spin qubit composed of two other parallel-connected MTJs and connected in parallel with the first spin qubit; and an entanglement wiring disposed between the first spin qubit and the second spin qubit and extending perpendicularly to a virtual plane formed by the first spin qubit and the second spin qubit.

[0024] According to the present invention described above, the spin qubit is composed of two parallel-connected MTJs and overlapping wiring arranged between the MTJs, or a single non-magnetic heavy metal layer in contact with the lower free layers of the two MTJs. A superposition of states of the spin qubit can be formed by applying a current through the overlapping wiring or by the direction of current flowing through the non-magnetic heavy metal layer.

[0025] Additionally, quantum entanglement between spin qubits can be implemented by arranging two spin qubits in parallel and through entanglement wiring between the spin qubits.

[0026] The quantum superposition and quantum entanglement described above are realized at room temperature. That is, current application using superposition wiring is performed at room temperature, and the superposition of states 0 and 1 is realized by the strength of the applied current. The observed value of the spin qubit is expressed as a combination of the probability functions of states 0 and 1. Furthermore, the states of parallel-connected spin qubits are determined by the current application through the entanglement wiring. This also has the advantage of operating at room temperature.

[0027] Through the above-described structure and operation, quantum superposition and quantum entanglement can be realized at room temperature.

[0028] Figure 1 is a perspective view for explaining the operation of qubits according to conventional superconducting technology.

[0029] FIG. 2 is a cross-sectional view of a spin qubit according to the first embodiment of the present invention.

[0030] FIG. 3 is a schematic diagram for defining the state of a spin qubit according to the first embodiment of the present invention.

[0031] FIG. 4 is a schematic diagram for explaining the state implementation of a spin qubit by an external magnetic field according to a second embodiment of the present invention.

[0032] FIG. 5 is a schematic diagram expressing the wires of FIG. 4 as a single wire according to the second embodiment of the present invention.

[0033] FIG. 6 is another schematic diagram for implementing the state of a spin qubit according to the second embodiment of the present invention.

[0034] Figure 7 is a schematic diagram for implementing quantum entanglement according to the third embodiment of the present invention.

[0035] FIG. 8 is a table for explaining the quantum entanglement of FIG. 7 according to the third embodiment of the present invention.

[0036] Figure 9 is another schematic diagram for implementing quantum entanglement according to a third embodiment of the present invention.

[0037] FIG. 10 is a table for explaining the quantum entanglement of FIG. 9 according to the third embodiment of the present invention.

[0038] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated in the drawings and described in detail herein. However, this is not intended to limit the present invention to a specific disclosed form, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0039] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0040] Hereinafter, with reference to the attached drawings, a preferred embodiment of the present invention will be described in more detail.

[0041]

[0042] Example 1: Definition of spin qubits and definition of states

[0043] FIG. 2 is a cross-sectional view of a spin qubit according to the first embodiment of the present invention.

[0044] Referring to Fig. 2, the spin cubic has a parallel connection structure of a first MTJ (100) and a second MTJ (200). In the present invention, MTJ refers to a magnetic tunnel junction structure, and magnetization reversal of the free layer within the MTJ is performed by an external magnetic field.

[0045] The first MTJ (100) has a first fixed magnetization induction layer (110), a first fixed layer (120), a first tunnel junction layer (130), and a first free layer (140).

[0046] The first fixed magnetization induction layer (110) is composed of two ferromagnetic layers (111, 113) and two RKKY (Ruderman-Kittel-Kasuya-Yosida) induction layers (112, 114). The first RKKY induction layer (112) is arranged between the first ferromagnetic layer (111) and the second ferromagnetic layer (113). Due to the thickness of the first RKKY induction layer (112), the first ferromagnetic layer (111) and the second ferromagnetic layer (113) form an antiferromagnetic coupling. The antiferromagnetic coupling refers to the magnetization of the first ferromagnetic layer (111) and the second ferromagnetic layer (113) being aligned in opposite directions, which is due to the RKKY interaction. Additionally, the second RKKY induction layer (114) is placed between the second ferromagnetic layer (113) and the first fixed layer (120) and forms a ferromagnetic coupling. Ferromagnetic coupling refers to the magnetization of two magnetically coupled ferromagnetic materials being set in the same direction.

[0047] The first fixed layer (120) forms a ferromagnetic bond with the second ferromagnetic layer (113) and follows the magnetization of the second ferromagnetic layer (113). In addition, a first tunnel junction layer (130) is formed under the first fixed layer (120), and a first free layer (140) is formed under the first tunnel junction layer (130).

[0048] In particular, the thickness of the first ferromagnetic layer (111) is set to be larger than the thickness of the second ferromagnetic layer (113). When a strong external magnetic field is applied while a constant temperature is applied during the manufacturing process, the first ferromagnetic layer (111) having the largest thickness aligns the magnetization in the direction of the external magnetic field. For example, assuming that the external magnetic field is applied upward, the first ferromagnetic layer (111) has upward magnetization. The second ferromagnetic layer (113) has downward magnetization due to antiferromagnetic coupling, and the first fixed layer (120) also has downward fixed magnetization due to ferromagnetic coupling.

[0049] The second MTJ (200) has a second fixed magnetization induction layer (210), a second fixed layer (220), a second tunnel junction layer (230), and a second free layer (240).

[0050] The second fixed magnetization induction layer (210) is composed of two ferromagnetic layers (211, 213) and two RKKY induction layers (212, 214). That is, the third RKKY induction layer (212) is arranged between the third ferromagnetic layer (211) and the fourth ferromagnetic layer (213). Due to the thickness of the third RKKY induction layer (212), the third ferromagnetic layer (211) and the fourth ferromagnetic layer (213) form an antiferromagnetic coupling. In addition, the fourth RKKY induction layer (214) is arranged between the fourth ferromagnetic layer (213) and the second fixed layer (220) and forms a ferromagnetic coupling.

[0051] In particular, the thickness of the fourth ferromagnetic layer (213) is set to be greater than the thickness of the third ferromagnetic layer (211). When an upward magnetic field is applied from the outside, the fourth ferromagnetic layer (213) having the largest thickness forms upward magnetization, and the second fixed layer (220) forming the ferromagnetic coupling also forms upward magnetization.

[0052] Therefore, the first fixed layer (120) of the first MTJ (100) and the second fixed layer (220) of the second MTJ layer (200) have fixed magnetizations in opposite directions. In addition, due to the RKKY interaction, the two fixed layers (120, 200) have perpendicular magnetic anisotropy in which the magnetization is perpendicular to the direction of the bonding surface or interface.

[0053] FIG. 3 is a schematic diagram for defining the state of a spin qubit according to the first embodiment of the present invention.

[0054] Referring to (a) of Fig. 3, it is assumed that the first fixed layer (120) of the first MTJ (100) has upward magnetization, and the second fixed layer (220) of the second MTJ (200) has downward magnetization. In the present invention, if the fixed layers of the spin qubit have magnetizations in opposite directions, it does not deviate from the spirit of the present invention.

[0055] When the magnetization of the free layers (140, 240) is set upward due to the influence of an external magnetic field, the first MTJ (100) enters a low-resistance state, and the second MTJ (200) enters a high-resistance state. The fixed layers (120, 220) are connected to each other through electrical wiring, and the free layers (140, 240) are also connected to each other through electrical wiring. Therefore, when a constant voltage is applied between the upper wiring and the lower wiring, current flows through the MTJs. However, the current flows only in the first MTJ (100) in the low-resistance state. Therefore, when viewed from the outside, the current in the spin qubit appears to flow counterclockwise. The above state is defined as state 1.

[0056] Referring to (b) of Fig. 3, the free layers (140, 240) have a downward magnetization state due to the application of an external magnetic field. The first MTJ (100) becomes a high-resistance state, and the second MTJ (200) becomes a low-resistance state. Accordingly, current flows through the second MTJ (200), and when viewed from the outside, the current appears to flow in a clockwise direction. The above condition is defined as state 0.

[0057] Referring to (c) of Fig. 3, the magnetization of the free layers (140, 240) is set in the horizontal direction due to the influence of the external magnetic field. When the magnetization of the free layer is set in the horizontal direction, the two MTJs (100, 200) have an intermediate resistance state regardless of the magnetization direction of the fixed layer, and the currents flowing through the two MTJs (100, 200) are identical to each other. This corresponds to a superposition state. That is, the horizontal magnetization of the free layers (140, 240) is interpreted as a phenomenon in which the upward magnetization and downward magnetization of the free layers (140, 240) are superimposed.

[0058] In the present invention, a state in which current flows in a clockwise direction is defined as state 0, a state in which current flows in a counterclockwise direction is defined as state 1, and a state in which current flows evenly through two MTJs due to horizontal magnetization of the free layer is defined as a superposition state.

[0059]

[0060] Example 2: Superposition in Spin Qubits

[0061] FIG. 4 is a schematic diagram for explaining the state implementation of a spin qubit by an external magnetic field according to a second embodiment of the present invention.

[0062] Referring to Fig. 4, a current emitted from the ground and a current flowing in toward the ground can be formed at the center of the spin cubic. That is, a first overlapping wire (151) emitted from the ground and a second overlapping wire (152) directed toward the ground are provided, and a current is applied through each overlapping wire (150), and an external magnetic field is artificially formed by the applied current.

[0063] That is, the overlapping wiring (150) has a configuration capable of applying an external magnetic field in a direction perpendicular to the interface of the junction to the free layers (140, 240) of the two MTJs (100, 200). Various forms of the overlapping wiring (150) can be used as long as it has a configuration capable of applying an external magnetic field in a direction perpendicular to the interface of the free layers (140, 240) and the tunnel junction layer (130, 230). In particular, the overlapping wiring (150) is arranged to extend in a direction perpendicular to an imaginary plane in which the first MTJ (100) and the second MTJ (200) are connected to each other in the stacked direction.

[0064] In addition, when current is discharged from the ground through the first overlapping wire (151), the current is directed toward the ground through the second overlapping wire (152), and when current is directed toward the ground through the first overlapping wire (151), the current is discharged from the ground through the second overlapping wire (152). Through the above configuration, the first overlapping wire (151) and the second overlapping wire (152) form magnetic fields in opposite directions. In addition, the first overlapping wire (151) is arranged adjacent to the first MTJ (100), and the second overlapping wire (152) is arranged adjacent to the second MTJ (200).

[0065] The initial state is assumed to be that the first free layer (140) is magnetized upward, and that the second free layer (240) is also magnetized upward. Therefore, the first MTJ (200) is in a low-resistance state, so the current flows counterclockwise and is in state 1.

[0066] When an intermediate level current flows through the first overlapping wire (151) and the second overlapping wire (152), the free layers (140, 240) have horizontal magnetization regardless of the direction of the current. Therefore, a superposition state is realized.

[0067] If a strong current is applied to the ground through the first overlapping wire (151), a counterclockwise external magnetic field is formed around the first overlapping wire (151), and the first free layer (140) has downward magnetization. In contrast, a clockwise external magnetic field is formed around the second overlapping wire (152), so the second free layer (240) also has downward magnetization. Accordingly, the second MTJ (200) has a low resistance state, and the first MTJ (100) has a high resistance state, so the current flowing through the spin qubit becomes clockwise, and state 0 is implemented.

[0068] The state of a spin qubit is determined by the current flowing through two wires, and the state can be expressed as a function of probability. That is, state 0 and state 1 can be expressed as probabilities through superposition.

[0069] FIG. 5 is a schematic diagram expressing the wires of FIG. 4 as a single wire according to the second embodiment of the present invention.

[0070] Referring to Fig. 5, the current directions flowing through the first overlapping wiring (151) and the second overlapping wiring (152) need to be set in opposite directions with respect to the ground. Therefore, the operation of Fig. 4 can be implemented by configuring the wiring to have a circular or approximately rectangular shape, setting the current inlet and outlet in the same area, and configuring the current to flow vertically through the interior of the spin qubit.

[0071] FIG. 6 is another schematic diagram for implementing the state of a spin qubit according to the second embodiment of the present invention.

[0072] Referring to Fig. 6, a non-magnetic heavy metal layer (105) is provided under the first MTJ (100) and the second MTJ (200). The non-magnetic heavy metal layer (105) is formed in contact with the free layer (140, 240). When the free layer (140, 240) of the MTJ element performs a magnetization reversal operation by spin-orbit torque, the magnetization of the free layer (120, 220) can be oriented upward or downward depending on the direction of the current flowing through the non-magnetic heavy metal layer (105).

[0073] That is, depending on the strength and direction of the current flowing through the non-magnetic heavy metal layer (105), the free layer can have an upward, downward, or horizontal magnetization state, thereby implementing state 0, state 1, and a superposition state.

[0074] For example, if the direction of the current flowing in the non-magnetic heavy metal layer (105) is to the right, the free layers (140, 240) have upward magnetization, and the first MTJ (100) becomes a low-resistance state and forms a counterclockwise internal current. Therefore, state 1 is implemented. If the direction of the current flowing in the non-magnetic heavy metal layer (105) is to the left, state 0 is implemented. In particular, if the current is below a certain threshold, the spin-orbit torque is not completely generated, so that an approximately horizontal magnetic moment is generated within the free layer (140, 240), and a superposition state is implemented.

[0075] As discussed in the second embodiment, the spin qubit is composed of two MTJs. The magnetization of the fixed layer in the two parallel-connected MTJs is set in the opposite directions, and the state of the spin qubit is realized by the wiring passing through the spin qubit, and the two states are in a superposition that can be derived from both probability functions. In particular, in addition to the wiring passing through the spin qubit, a non-magnetic heavy metal layer crossing the lower part of the free layers can be arranged, and a spin-orbit torque can be induced to invert or change the magnetization of the free layer, thereby realizing a superposition state.

[0076]

[0077] Example 3: Implementation of quantum entanglement between spin qubits

[0078] In this embodiment, to explain quantum entanglement, it is explained that each spin qubit is preset to state 1 or state 0 by superposition wiring or a non-magnetic heavy metal layer. Quantum entanglement is the principle that when the state of one qubit is confirmed, the state of the other qubit is confirmed, which is a different concept from the concept of a state being transferred to another qubit. In other words, the states of the two qubits are already determined, and the principle is that if the state of one is known, the state of the other is automatically known.

[0079] In addition, this embodiment explains that the state of another unobserved spin qubit is determined by the arrangement structure of the spin qubit and the direction of application of the entanglement current.

[0080] FIG. 7 is a schematic diagram of a quantum entanglement structure using a spin qubit that implements quantum entanglement according to a third embodiment of the present invention.

[0081] Referring to Fig. 7, two spin qubits (600, 700) connected in parallel with each other and an entanglement wiring (500) between the spin qubits (600, 700) are arranged. In addition, a superposition wiring is arranged inside each spin qubit (600, 700) as described in the second embodiment, thereby implementing quantum superposition.

[0082] The first spin qubit (600) has two MTJs (100, 200) and has a superposition state by means of overlapping wiring or a non-magnetic heavy metal layer as described in the second embodiment. For convenience of explanation, the orientation of the free layers of the MTJs is defined as either upward or downward.

[0083] Additionally, the second spin qubit (700) also has two MTJs (300, 400) and is defined as being set to a specific state by the MTJs.

[0084] However, in FIG. 7, the two spin qubits (600, 700) have the same structure. In this embodiment, the fact that the spin qubits (600, 700) have the same structure means that the magnetization arrangements of the fixed layers are the same. For example, the magnetization direction of the fixed layer of the first MTJ (100) of the first spin qubit (600) is the same as the magnetization direction of the fixed layer of the third MTJ (300) of the second spin qubit (700) corresponding to the fixed layer. Similarly, the magnetization direction of the fixed layer of the second MTJ (200) of the first spin qubit (600) is the same as the magnetization direction of the fixed layer of the fourth MTJ (400) of the second spin qubit (700) corresponding thereto. That is, the two spin qubits (600, 700) have a structure in which they are repeatedly arranged.

[0085] In addition, an entanglement wiring (500) is arranged between two spin qubits (600, 700). The entanglement wiring (500) has a first entanglement wiring (510) and a second entanglement wiring (520). In addition, the state of the spin qubit is preset by the strength and direction of the current supplied through the entanglement wiring (500). Therefore, after a current is applied through the entanglement wiring (500), when the state of one spin qubit is observed, the state of the other spin qubit can be determined without an observation operation.

[0086] The above entanglement wiring (500) extends in a direction perpendicular to a virtual plane (ground) formed by two spin qubits (600, 700) and forms an external magnetic field in a direction perpendicular to the free layers of the spin qubits (600, 700).

[0087] For quantum entanglement, the first entanglement wire (510) is arranged close to the first spin qubit (600), and the second entanglement wire (520) is arranged close to the second spin qubit (700). In addition, the strength of the magnetic field generated by the current flowing through the entanglement wire (500) has a characteristic of being inversely proportional to the square of the distance. Therefore, through the arrangement of the wires, the magnetic field generated in the first entanglement wire (510) controls the magnetization of the free layers of the first spin qubit (600), and the magnetic field generated in the second entanglement wire (520) controls the magnetization of the free layers of the second spin qubits (700).

[0088] FIG. 8 is a table for explaining the quantum entanglement of FIG. 7 according to the third embodiment of the present invention.

[0089] Referring to FIGS. 7 and 8, quantum entanglement has two operation modes. The first operation is an operation in which two spin qubits (600, 700) have the same state and reverse the state depending on the strength and direction of the applied current, which is described as the operation of entanglement 1. The second operation is an operation in which two spin qubits (600, 700) have different states and reverse the states depending on the applied current, which is described as the operation of entanglement 2.

[0090] When the state of the first spin qubit (600) is changed in an entangled state, the state of the second spin qubit (700) also changes. When the direction of the current is adjusted to implement a desired state in one spin qubit, the state of the other spin qubit is determined dependently.

[0091] The operation of entanglement 1 is when two spin qubits (600, 700) are in the same state. A current flows in the direction (ⓧ) toward the ground through the first entanglement wire (510), and a current flows in the direction (⊙) away from the ground through the second entanglement wire (520). Therefore, a strong upward external magnetic field is applied to the first spin qubit (600) and the second spin qubit (700), and the free layers have an upward magnetic moment. Therefore, when viewed from the outside, the first spin qubit (600) has a counterclockwise internal current due to the first MTJ (100) in a low-resistance state and the second MTJ (200) in a high-resistance state, and the second spin qubit (700) also has a counterclockwise internal current due to the third MTJ (300) in a low-resistance state and the fourth MTJ (400) in a high-resistance state.

[0092] In the above state, if the direction of the current of the entanglement wiring (500) is reversed, the states of the first spin qubit (600) and the second spin qubit (700) are reversed. That is, the states of the first spin qubit (600) and the second spin qubit (700) are reversed depending on the direction of the current, so that both have state 0.

[0093] The operation of the above entanglement 1 can be implemented by short-circuiting the entanglement wires (500). That is, the operation can be realized by opening two terminals on the ground side and short-circuiting two terminals inside the ground so that the current flowing into the first entanglement wire (510) flows out to the second entanglement wire (520).

[0094] The operation of entanglement 2 is when the states of the first spin qubit (600) and the second spin qubit (700) are different. First, it is assumed that the state of the first spin qubit (600) is 1 and the state of the second spin qubit (700) is 0.

[0095] In the above state, when a current flowing into the ground in the same direction is supplied to the first entanglement wire (510) and the second entanglement wire (520), an upward external magnetic field is applied to the first spin qubit (600), thereby setting the magnetic moment of the free layer of the first spin qubit (600) in the upward direction. In addition, since a downward external magnetic field is applied to the second spin qubit (700), the magnetic moment of the free layer of the second spin qubit (700) is aligned in the downward direction. Therefore, the state of the first spin qubit (600) is set to 1, and the state of the second spin qubit (700) is set to 0.

[0096] If the direction of the current is reversed through the entanglement wiring (500) in the above state, the state of each spin qubit is also reversed.

[0097] The above operation can be implemented by short-circuiting two terminals of the ground portion of the first entanglement wire (510) and the second entanglement wire (520), and short-circuiting two invisible terminals inside the ground portion. In addition, the entanglement 2 operation can be implemented using a single wire instead of two wires.

[0098] Figure 9 is another schematic diagram for implementing quantum entanglement according to a third embodiment of the present invention.

[0099] Referring to Fig. 9, two spin qubits (600, 700) connected in parallel with each other and an entanglement wiring (500) between the spin qubits (600, 700) are arranged. In addition, a superposition wiring is arranged inside each spin qubit (600, 700) as described in the second embodiment, thereby implementing quantum superposition. This is the same as described in Fig. 7.

[0100] However, in FIG. 9, the two spin qubits (600, 700) have a mutually symmetrical structure. In this embodiment, the fact that the spin qubits (600, 700) have a symmetrical structure means that the magnetization arrangements of the fixed layers are symmetrical. For example, the magnetization direction of the fixed layer of the first MTJ (100) of the first spin qubit (600) is the same as the magnetization direction of the fixed layer of the fourth MTJ (400) of the second spin qubit (700), which is symmetrical to the first MTJ (100). Similarly, the magnetization direction of the fixed layer of the second MTJ (200) of the first spin qubit (600) is the same as the magnetization direction of the fixed layer of the third MTJ (300) of the corresponding second spin qubit (700). That is, the two spin qubits (600, 700) are arranged facing each other.

[0101] Additionally, an entanglement wiring (500) is placed between two spin qubits (600, 700), which is the same as described in FIG. 7 above.

[0102] FIG. 10 is a table for explaining the quantum entanglement of FIG. 9 according to the third embodiment of the present invention.

[0103] Referring to FIGS. 9 and 10, during initial operation, the current flowing through the first entanglement wire (510) is set to be directed toward the ground, and the current flowing through the second entanglement wire (520) is set to flow out from the ground. Accordingly, an upward external magnetic field is applied to the first MTJ (100) and the second MTJ (200), and an upward external magnetic field is also applied to the third MTJ (300) and the fourth MTJ (400) within the second spin qubit (700). Accordingly, the first spin qubit (600) forms a counterclockwise internal current and becomes state 1, and the second spin qubit (700) forms a clockwise internal current and has state 0.

[0104] When the direction of the current flowing through the entanglement wiring (500) is reversed in the above state, the first spin qubit (600) has state 0, and the second spin qubit (700) has state 1.

[0105] That is, in entanglement 1, the directions of the current flowing through the first entanglement wire (510) and the current flowing through the second entanglement wire (520) are opposite to each other, and this can be implemented through a configuration that allows the current flowing into the first entanglement wire (510) to flow out to the second entanglement wire (520) as described in FIG. 8.

[0106] Looking at the operation of the above entanglement 1, the aspect of the operation can be determined depending on the arrangement state of the spin qubits (600, 700). That is, in the case of the arrangement structure of the spin qubits (600, 700) in FIG. 7, the first spin qubit (600) and the second spin qubit (700) can repeat the same state depending on the direction of the current. However, in the arrangement structure of FIG. 9, the first spin qubit (600) and the second spin qubit (700) can alternately have different states.

[0107] In any case, a person skilled in the art can preset the state of entanglement through the arrangement structure of the spin qubits (600, 700), and by observing the state of the first spin qubit (600) only by the current applied to the entanglement wiring (500), the state of the second spin qubit (700) can be obtained without observation.

[0108] In the state of entanglement 2, it can be implemented with a single entanglement wire as mentioned in the above-mentioned Fig. 8, and the first entanglement wire (510) and the second entanglement wire (520) supply current in the same direction.

[0109] When current is introduced to the ground through the first entanglement wire (510) and the second entanglement wire (520), an upward external magnetic field is formed in the first spin qubit (600), and the magnetic moments of the free layers are oriented upward to implement state 1. In addition, a downward external magnetic field is formed in the second spin qubit (700), thereby implementing state 1.

[0110] In the above state, when a current flowing to the ground through the first entanglement wire (510) and the second entanglement wire (520) is generated, a downward external magnetic field is applied to the first spin qubit (600), and an upward external magnetic field is applied to the second spin qubit (700). Accordingly, the state of the first spin qubit (600) changes to 0, and the state of the second spin qubit (700) also changes to 0.

[0111] If the operation of the above-described entanglement 2 is explained with reference to FIG. 8, the state of the spin qubit on the other side is known in advance depending on the arrangement state of the spin qubit. That is, when the same structure is repeated as in FIG. 8, the first spin qubit (600) and the second spin qubit (700) have different states, and the different states can be determined through one type of current applied through the entanglement wiring (500). In addition, when two spin qubits (600, 700) are arranged in a symmetrical structure as in FIG. 10, the state of the other spin qubit can be known in advance as a different state from the observed spin qubit through one type of current applied through the entanglement wiring (500).

[0112]

[0113] As described above, the spin qubit of the present invention is composed of two parallel-connected MTJs and overlapping wiring arranged between the MTJs, or a single non-magnetic heavy metal layer in contact with the lower free layers of the two MTJs. A superposition of the states of the spin qubit can be formed by the current applied through the overlapping wiring or the direction of the current flowing through the non-magnetic heavy metal layer.

[0114] Additionally, quantum entanglement between spin qubits can be implemented by arranging two spin qubits in parallel and through entanglement wiring between the spin qubits.

[0115] The quantum superposition and quantum entanglement described above are realized at room temperature. That is, current application using superposition wiring is performed at room temperature, and the superposition of states 0 and 1 is realized by the strength of the applied current. The observed value of the spin qubit is expressed as a combination of the probability functions of states 0 and 1. Furthermore, the states of parallel-connected spin qubits are determined by the current application through the entanglement wiring. This also has the advantage of operating at room temperature.

[0116] Through the above-described structure and operation, quantum superposition and quantum entanglement can be realized at room temperature.

Claims

1. A first MTJ having a first free layer, a first tunnel junction layer formed on the first free layer, and a first fixed layer formed on the first tunnel junction layer; A second MTJ having a second free layer, a second tunnel junction layer formed on the second free layer, and a second fixed layer formed on the second tunnel junction layer; and An overlapping wiring disposed between the first MTJ and the second MTJ, having a first overlapping wiring adjacent to the first MTJ and a second overlapping wiring adjacent to the second MTJ, wherein the directions of current flowing through the first overlapping wiring and the second overlapping wiring are opposite to each other, A spin qubit characterized in that the first MTJ and the second MTJ are connected in parallel with each other, the magnetization directions of the first fixed layer and the second fixed layer are opposite to each other, and the overlapping wiring extends in a direction perpendicular to an imaginary plane connecting the growth directions of the first MTJ and the second MTJ.

2. A spin qubit according to claim 1, wherein the first fixed layer and the second fixed layer have perpendicular magnetic anisotropy.

3. A spin qubit according to claim 1, characterized in that the first free layer and the second free layer have magnetization states in the same direction due to a current flowing through the overlapping wiring.

4. A spin qubit according to claim 3, characterized in that the current flowing into the first overlapping wiring flows out into the second overlapping wiring.

5. A spin qubit according to claim 4, characterized in that quantum superposition occurs between the first free layer and the second free layer by a current flowing through the overlapping wiring.

6. A first MTJ having a first free layer, a first tunnel junction layer formed on the first free layer, and a first fixed layer formed on the first tunnel junction layer; A second MTJ having a second free layer, a second tunnel junction layer formed on the second free layer, and a second fixed layer formed on the second tunnel junction layer; and It includes a non-magnetic heavy metal layer that is commonly connected to the lower portions of the first free layer and the second free layer and induces a spin-orbit torque in the first free layer and the second free layer to control the magnetization state of the first free layer and the second free layer, A spin qubit characterized in that the first MTJ and the second MTJ are connected in parallel with each other, and the magnetization directions of the first fixed layer and the second fixed layer are opposite to each other.

7. A spin qubit characterized in that the first free layer and the second free layer have magnetization states in the same direction due to a current flowing through the non-magnetic heavy metal layer.

8. A spin qubit according to claim 7, characterized in that the first free layer and the second free layer have a superposition state of horizontal magnetization due to a current flowing through the non-magnetic heavy metal layer. A first spin qubit consisting of 9.2 parallel-connected MTJs; a second spin qubit, which is composed of two other parallel-connected MTJs and is parallel-connected to the first spin qubit; and A quantum entanglement structure of spin qubits, comprising an entanglement wiring disposed between the first spin qubit and the second spin qubit and extending perpendicularly to a virtual plane formed by the first spin qubit and the second spin qubit.

10. In the 9th paragraph, the two MTJs constituting the first spin qubit and the second spin qubit each have a free layer, a tunnel junction layer formed on the free layer, and a fixed layer formed on the tunnel junction layer. A quantum entanglement structure of a spin qubit, characterized in that the magnetization of the above-mentioned fixed layer has perpendicular magnetic anisotropy.

11. A quantum entanglement structure of a spin qubit, characterized in that the fixed layers of the two MTJs of the first spin qubit or the second spin qubit in the 10th paragraph have magnetization states in opposite directions.

12. A quantum entanglement structure of a spin qubit, characterized in that the free layers of the two MTJs in the 11th paragraph have magnetization states in the same direction.

13. A quantum entanglement structure of a spin qubit, characterized in that in the 12th paragraph, the first spin qubit or the second spin qubit includes an overlapping wiring arranged between the two MTJs, and the overlapping wiring extends vertically to a virtual plane in which the two MTJs are formed.

14. A quantum entanglement structure of a spin qubit, characterized in that in the 13th paragraph, the overlapping wiring has a first overlapping wiring that forms an external magnetic field that controls magnetization of a free layer in proximity to one of the two MTJs and a second overlapping wiring that controls magnetization in proximity to the other of the two MTJs, and currents flowing through the first overlapping wiring and the second overlapping wiring are in opposite directions.

15. A quantum entanglement structure in accordance with claim 12, wherein the two MTJs have a non-magnetic heavy metal layer formed under the free layers and connected in common to the free layers, and a spin-orbit torque is formed in the free layers by a current flowing through the non-magnetic heavy metal layer.

16. In the 9th paragraph, the entangled wiring is A first entanglement wire adjacent to the first spin qubit that controls the magnetization direction of the free layers of the first spin qubit; and A quantum entanglement structure of a spin qubit, characterized in that it includes a second entanglement wiring adjacent to the second spin qubit and controlling the magnetization direction of the free layers of the second spin qubit.

17. A quantum entanglement structure in claim 9, characterized in that the magnetization directions of the fixed layers of the two parallel-connected MTJs of the first spin qubit have the same repeating structure as the magnetization directions of the fixed layers of the two parallel-connected MTJs of the second spin qubit.

18. A quantum entanglement structure in claim 9, characterized in that the magnetization directions of the fixed layers of the two parallel-connected MTJs of the first spin qubit have a structure symmetrical to each other.

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