Quantum memory unit and quantum register

Abstract

The present invention relates to a quantum memory unit (100) comprising a nanodiamond (120) having a quantum emitter (140), wherein the electron spin of the quantum emitter (140) is coupled to a spin body (170) inside or outside the nanodiamond (120), the coupling rate of the electron spin to the spin body (170) is greater than the decoherence rate of the electron spin, and the spin body (170) is designed and configured to be able to store quantum information inside, to be able to retrieve said quantum information, and / or to be able to manipulate the quantum state of said spin body (170).

Description

Technical Field

[0001] The present invention relates to a quantum memory unit and a quantum register.

[0002] In the prior art, many different systems have been used to realize quantum memory, but most of them have the drawback of falling into decoherence.

[0003] Decoherence or quantum decoherence is understood to be the loss of quantum coherence. In quantum mechanics, particles are described by wave functions. As long as there is a clear phase relationship between different states, the system is called coherent. Such a clear phase relationship is necessary for performing quantum calculations on quantum information encoded in quantum states. When a quantum system is completely isolated, coherence is maintained for an indefinite length, but it is impossible to operate or investigate it. When the quantum system is not completely isolated, for example during measurement, coherence is shared with the environment and seems to be lost over time. The process is called quantum decoherence or environmental decoherence.

[0004] In the prior art, a method for manufacturing a nanodiamond is known. A nanodiamond having an SiV - center is known to be able to be manufactured by a chemical vapor deposition (CVD) method or a high pressure high temperature (HPHT) manufacturing method.

[0005] The problem of the present invention is to improve the prior art. In particular, an object of the present invention is to provide a quantum memory unit having a lower decoherence rate than the prior art.

[0006] As another object of the present invention, on the one hand, it is to provide a quantum memory unit that can efficiently couple to flying qubits with a long coherence time, and on the other hand, can securely store quantum information in a long-lived quantum memory inside the quantum memory unit.

[0007] Another objective of the present invention is to provide a quantum memory unit that can be realized inside nanodiamonds.

[0008] Another object of the present invention is to modify the phonon interaction within the nanodiamond host crystal using strain within the nanodiamond, particularly intrinsic strain, so as to suppress the decoherence of the electron spin of the quantum emitter.

[0009] Another object of the present invention is to provide a quantum device that can realize a quantum register, in particular perform quantum computations, and implement quantum algorithms.

[0010] Furthermore, another objective of the present invention is to enable the functioning of a quantum memory unit that can be incorporated into a cavity by electromagnetic coupling, such as optical coupling.

[0011] The object of the present invention is solved by a quantum memory unit having the features of independent claim 1. Preferred embodiments of the present invention are disclosed in each dependent claim.

[0012] A quantum memory unit is understood to be a device capable of storing and retrieving quantum information without losing coherence or fidelity on a time scale relevant to a particular application.

[0013] Nanodiamonds are understood to be diamond particles so small that they can be measured in nanometer units, meaning their size is less than 1000 nm. Particle size is understood to be the maximum range of particles along a given axis when measured in different coordinate systems.

[0014] A quantum emitter can be understood as a quantum system capable of radiative phototransitions. Observing the spontaneous decay of a single-excited quantum emitter suggests the emission of a single photon. If non-radiative decay mechanisms are suppressed, the quantum emitter can essentially function as a 100% efficient single-photon source. A variety of systems provided by nature enable numerous possible experiments and implementations for photonic applications. Quantum emitters can be, for example, single atoms in high-resolution cavities, colloidal nanocrystals of different sizes, color centers in solids, quantum dots, or nanowire quantum dot structures. Quantum emitters can be used, for example, to realize qubits (Q-bits) or to connect the states of Q-bits to optical channels. A Q-bit is a two-state quantum mechanical system that can exist as a superposition of two ground states, usually described as |0> and |1>.

[0015] A spin body is a physical object that possesses spin properties. A spin body has a magnetic moment that interacts with a magnetic field. A spin body can be, or may include, the electron spin of an atom, the electron spin of a color center, or the electron spin of a defect center, and / or the nuclear spin of an atomic nucleus. A spin body can also include two or more coupled spin bodies, such as two or more electron spins. The resulting coupled spin is referred to as the total spin (S) or net spin of the system. Preferably, the absolute value or modulus of the total spin S of the spin body is 1 / 2 or greater.

[0016] Spin bodies can be manipulated and measured using various techniques, such as electron spin resonance (ESR), which involve inducing transitions between different spin states of electrons in a sample using microwaves.

[0017] The spin body can be located inside or outside the nanodiamond. If the spin body is located outside the nanodiamond, it is preferable that it is located in the vicinity of the nanodiamond, for example, on or adjacent to the surface of the nanodiamond. Here, the term "outside the diamond" includes the meaning of "on the surface of the diamond."

[0018] Here, the term "electron spin" is understood to refer to the electron spin of the quantum emitter. Both the decoherence of electron spin and the decoherence of the spin body contribute to the decoherence rate of the coupled spin system. The decoherence of electron spin is considered to be a limiting factor for the decoherence of the coupled spin system. Therefore, in the following, unless otherwise specified, the decoherence rate of the coupled system will generally be referred to as the decoherence rate of electron spin.

[0019] The characteristic that the coupling rate between the electron spin and the spin body is greater than the decoherence rate of the electron spin means that the quantum information stored within the electron spin can be transferred to the spin body before the information stored within the electron spin is destroyed due to the decoherence of the electron spin. This characteristic requires that quantum information be effectively transferred between the electron spin and the spin body of the quantum emitter.

[0020] A spin body is designed and configured to be able to store quantum information internally, to be able to retrieve that quantum information, and / or to be able to manipulate the quantum state of the spin body. This feature is equivalent to the requirements often imposed on Q bits, namely, the requirement to be able to write quantum information to a Q bit, to be able to read it from a Q bit, and to be able to manipulate the quantum state of a Q bit.

[0021] This can be achieved using various methods. According to the first method, quantum information stored in a quantum emitter can be transferred to the spin body by using the coupling between the spin body and the electron spin of the quantum emitter. According to the second method, the quantum state of a flying Q-bit can be transferred to the quantum emitter, and then the quantum state of the quantum emitter can be transferred to the spin body.

[0022] The central idea of ​​this invention is to use one part of the system, namely the spin body, as a long-lived quantum memory, based on the coupling, preferably strong coupling, between a quantum emitter in a nanodiamond, for example, the electron spin of a color center, and a spin body inside or outside the nanodiamond, and the other part of the system, namely the quantum emitter within the nanodiamond, as a possible quantum communication device to the outside world, such as a flying Q-bit. The advantage here is that, as already mentioned, the electron spin of the quantum emitter can easily exchange quantum information from outside the nanodiamond with, for example, a flying Q-bit. The quantum emitter inside the nanodiamond functions as a quantum communication interface to the outside world of the nanodiamond. The spin body inside the nanodiamond is fairly well shielded from the outside world, that is, the decoherence rate of the quantum state of the spin body is lower than the decoherence rate experienced by other quantum bodies around the spin body.

[0023] A further advantage of the present invention is that the coupling of the electron spin of the quantum emitter with the spin body enables effective exchange of quantum information between the electron spin of the quantum emitter and the long-lived and well-insulated spin body.

[0024] Another advantage of the present invention is that quantum memory units, in particular the spin bodies of quantum memory units, can be incorporated into a solid matrix having dimensions that allow for effective external coupling, such as optical coupling, i.e., in this case, into a diamond.

[0025] Another advantage of the present invention is that, in particular, the efficient external coupling of the spin bodies enables efficient information transfer of the spin bodies, for example, to or from flying Q bits inside or outside the nanodiamonds, or to another spin body.

[0026] Another advantage of the present invention is that the small size of the nanodiamond or quantum memory unit allows for the integration of the quantum memory unit into devices, such as tuned photonic structures and / or microwave structures.

[0027] A further advantage of the present invention is that the small size of the nanodiamond or quantum memory unit allows for the suppression of electron-phonon coupling, thereby improving the electron spin coherence time.

[0028] According to a preferred embodiment of the quantum memory unit, the spin body is the non-zero nuclear spin of an atom. The atom may be an atom of nanodiamond, i.e., one inside the nanodiamond, or one outside the nanodiamond.

[0029] The advantage of this feature is that the quantum information stored within the nuclear spin is well isolated from its environment, which means that the decoherence rate of the quantum information stored within the nuclear spin is extremely low. Nuclear spins can generally be well isolated from their environment because their interaction rate with the spin environment is smaller than that of the corresponding interaction rate of electron spins. This is due to the fact that the magnetic moment of the nuclear spin is smaller than that of the electron spin. Furthermore, in diamond, the environment can be purified isotropically, further reducing the decoherence mechanism induced by the environment. This makes extremely long storage times possible, for example, longer than 1 ms.

[0030] Because the quantum emitter is located within the diamond matrix of the nanodiamond, the spin body density in the environment, such as the concentration of carbon-13 isotopes, can be controlled during nanodiamond synthesis.

[0031] On the one hand, it is preferable that there are not an excessive number of spin bodies inside the nanodiamond so that the possibility of spin bodies decomposing still exists. On the other hand, it is preferable that there are not an excessively small number of spin bodies inside the nanodiamond so that there are still a sufficient number of spin bodies to observe.

[0032] Within the nanodiamond, it is preferable that there are few spin bodies with different bonding strengths, and that each spin body is coupled to the electron spin of the quantum emitter. This is because it is possible to realize a Q-bit quantum register in this manner. This will be explained later in this specification.

[0033] The atoms are preferably carbon-13 isotopes, Si-29 isotopes, N-15 isotopes, or atoms inside or outside nanodiamonds having non-zero nuclear spin.

[0034] According to another preferred embodiment of the quantum memory unit, the spin body is an electron spin body. An electron spin body is understood to be an object containing electron spins obtained from a single electron spin or a plurality of coupled electron spins.

[0035] In the absence of a magnetic field, the ground state of a quantum emitter is energetically divided due to the interaction between the electron spin of the quantum emitter and its orbital angular momentum, as well as the interaction between the orbital angular momentum and static strain. This energy difference is called the orbital ground state decomposition.

[0036] In the presence of a magnetic field, the orbital ground state described above is divided into spin states due to the interaction between the external magnetic field and the magnetic moment of the spin state; this is called spin state decomposition. The spin state is further divided into composite spin states due to the interaction between a spin body or multiple spin bodies and the magnetic moment. The energy difference between these states is called the composite spin state decomposition. When the spin body is a nuclear spin, the composite spin state decomposition corresponds to hyperfine decomposition.

[0037] The magnetic field strength inside the nanodiamond is preferably greater than 50 mT. More preferably greater than 300 mT. Even more preferably, the magnetic field inside the nanodiamond is formed by preferably four permanent magnets in a Halbach array or Halbach arrangement. The Halbach array is designed for a magnetic field strength of about 400 mT, i.e., preferably 390-410 mT.

[0038] A subset of two states, either a spin state or a compound spin state, can also be used as a Q bit.

[0039] The quantum state of a Q-bit can be directly and / or indirectly manipulated and controlled by electromagnetic interactions, such as light waves and / or microwave and / or RF frequencies.

[0040] The term "optical control" includes coupling two Q-bit states using Raman transitions via excited states. The energy difference between the Q-bit state and the aforementioned excited state may be within the optical range.

[0041] According to different preferred embodiments, the strain of the nanodiamond is greater than a predetermined value such that the ground state resolution, preferably the orbital ground state resolution, is greater than 46 GHz. Herein, the value is such that the quantum emitter is SiV - This concerns the central quantum memory unit. This feature advantageously allows for a reduction in the electron spin decoherence rate of the quantum emitter, particularly to a value below 4 MHz. Preferably, this is achieved at a temperature of 4 K. At liquid helium temperatures, the phonon absorption rate becomes the final limiting factor for the electron spin decoherence rate. The phonon absorption rate is a function of the strain-dependent orbital ground state partitioning.

[0042] The electron spin coherence time T2 in a quantum emitter, particularly at a color center, is a characteristic time with respect to the loss of phase coherence of electron spin in the presence of a magnetic field.

[0043] If the dimensions of the nanodiamonds are smaller, the orbital T1 time may become longer as the cutoff frequency obtained in the phonon density of states begins to act on the occupancy of phonons at the relevant phonon energy. An increase in orbital T1 can lead to an increase in the electron spin coherence time T2.

[0044] Time T1 is the characteristic time for relaxation of the ground state to thermal equilibrium. Orbital time T1 is the characteristic time for relaxation of the orbital ground state to thermal equilibrium. Spin time T1 is the characteristic time for relaxation of the spin ground state to thermal equilibrium.

[0045] At liquid helium temperatures, the decoherence rate of electron spins in nanodiamonds is primarily limited by phonon-mediated decoherence.

[0046] Phonon-mediated decoherence can be improved by cooling nanodiamonds to mK temperature to alter the phonon density of states (PDOS), or by increasing the ground state resolution of the quantum emitter to suppress phonon absorption. PDOS is a function that represents the number of phonons per vibrational mode or unit frequency range in a solid or liquid.

[0047] More preferably, the strain of the nanodiamond is greater than another predetermined value such that the ground state resolution, preferably the orbital ground state resolution, is greater than 0.5 THz. This feature advantageously enables a further reduction in the decoherence rate of the electron spins of the quantum emitter.

[0048] For orbital ground state resolutions greater than 0.5 THz, the corresponding electron spin coherence rate Γ² can be less than 320 kHz. This was extrapolated from coherent population trap (CPT) measurements.

[0049] For orbital ground state resolutions greater than 1 THz, the corresponding electron spin coherence rate Γ² can be reduced to less than 160 kHz. This was extrapolated from the Ramsey measurement method. The corresponding electron spin coherence rate Γ², extrapolated from the Hahn echo measurement, can be reduced to less than 16 kHz. The electron spin coherence rate Γ², extrapolated from the XY-N measurement, can be reduced to less than 5 kHz.

[0050] Due to the characteristics described above, phonon absorption by the quantum emitter is advantageously reduced, and the decoherence of the quantum emitter, particularly the decoherence of the Q-bit realized through the quantum emitter, is advantageously achieved.

[0051] According to a preferred embodiment, the size of the nanodiamonds is smaller than the wavelength of the optical transition of the quantum emitter.

[0052] This feature advantageously enables efficient coupling of an electric field to a quantum emitter located inside the nanodiamond. This electric field can be the electric field of a resonator or cavity. This means that flying Q-bits can be efficiently coupled to the quantum emitter.

[0053] The size of the nanodiamonds is more preferably less than 100 nm. Even more preferably less than 30 nm.

[0054] In addition to or instead of the preferred embodiments described above, the size of the nanodiamond is smaller than the wavelength of the phonon in the nanodiamond corresponding to the ground state resolution energy.

[0055] As a result, the PDOS exhibits a monotonically increasing behavior with stepped cutoff frequencies, such that PDOS below the cutoff frequency is suppressed compared to bulk diamond, or it has a spectral region in which PDOS is suppressed compared to bulk diamond. Here, the transition frequency corresponding to the orbital ground state division of the quantum emitter is smaller than the aforementioned cutoff frequency or falls within the spectral region. This essentially has the effect that phonons are not absorbed by transitions between ground states. Therefore, phonons corresponding to the energy of the ground state division cannot propagate inside the nanodiamond due to the small size of the nanodiamond. Consequently, the number of phonons inside the nanodiamond is reduced, which can trigger transitions between ground states. From this, the above-mentioned characteristics favorably lead to reduced phonon absorption of the quantum emitter, a longer orbital T1 time, and a reduction in the decoherence of the quantum emitter, particularly the decoherence of the Q-bit realized through the quantum emitter.

[0056] According to another preferred embodiment, the quantum emitter is a group IV color center, preferably a negatively charged single silicon vacancy (SiV). - It is the center.

[0057] For example, negatively charged nitrogen vacancy centers (NV) within diamond - The first small network based on ) has been realized in pioneering research, NV - It is easily perturbed by external fields and possesses only a low percentage of coherent photons.

[0058] In contrast, Group IV defects, particularly negatively charged silicon vacancy centers (SiV), - ) has the advantage that its atomic transition frequency is insensitive to an external electric field and that it has essentially the same emitter. Negatively charged single silicon vacancy SiV - Using the center is advantageous because it has higher luminescence, a narrower linewidth, and better spectral stability.

[0059] According to a different preferred embodiment, the quantum memory unit further has a second spin body outside the nanodiamond, where the electron spin of the quantum emitter is coupled to the spin of the second spin body, and the coupling rate of the spin of the spin body to the electron spin of the quantum emitter is greater than the decoherence rate of the electron spin of the quantum emitter.

[0060] The use of coupling between a second spin body outside the nanodiamond and the electron spin of a quantum emitter inside the nanodiamond has the advantage that quantum information stored inside the nanodiamond can be coupled to an external quantum platform, such as superconducting technology, thereby forming interfaces between different processor units and / or memory units.

[0061] Another advantage of this feature is that the coupled spin bodies are not necessarily coupled to the optical field, or more generally, not to the electromagnetic field. This is advantageous because it results in low decoherence.

[0062] The second spin body is preferably located near the nanodiamond, for example, on or adjacent to the surface of the nanodiamond.

[0063] The second spin body outside the nanodiamond could be, for example, a magnetic nanoparticle, a single-molecule magnet, or a nuclear spin.

[0064] According to another embodiment, the coupling rate of electron spins to the spin body is greater than 0.01 MHz, preferably greater than 0.1 MHz, and more preferably greater than 5 MHz. Even more preferably, the coupling here is greater than 40 MHz.

[0065] The advantage of this feature is that, due to its strong coupling ratio, indirect manipulation of spin bodies via electron spin can be performed on a faster timescale.

[0066] A further advantage of this feature is that, for a given decoherence rate, as the coupling strength increases, the maximum number of operating cycles per decoherence time also increases.

[0067] Yet another advantage of this feature is that it allows for easier detection of spin species without the need for a decoupling scheme and without increasing the electron spin decoherence time.

[0068] According to yet another preferred embodiment, the decoherence rate of the electron spin is smaller than the electron spin flip rate during driving. The electron spin flip rate during driving is a measure of how fast the spin state of an electron changes when the electron's spin state is subjected to an external driving force, such as an electric field, such as an electromagnetic pulse, a magnetic field, and / or an optical field. This feature advantageously enables efficient processing of the quantum information stored within the electron spin. This is because the processing speed, i.e., the electron spin flip rate, is faster than the decoherence rate that includes spontaneous emission as a limiting factor.

[0069] SiV as a quantum emitter - In a quantum memory unit having a center, the electron spin flip rate during driving may be, for example, about 10 MHz, preferably 5 - 15 MHz.

[0070] According to a preferred embodiment, the transition of the quantum emitter is driven by microwave radiation and / or optical radiation. Microwave and optical radiation are standard and widely available means.

[0071] Negatively charged single silicon vacancy SiV - In the case of a nanodiamond having a center with a negatively charged single silicon vacancy SiV as a quantum emitter, where the electron spin is coupled to the nuclear spin of carbon-13 isotope, it is preferred that the decoherence rate of the electron spin is less than 320 kHz. The value here is an actual measured value of the present invention. This represents a decoherence rate that is approximately 10 times lower compared to the known prior art measurements of bulk diamond at a similar temperature where the decoherence rate is 4.5 MHz.

[0072] In another embodiment, the quantum memory unit is designed and configured such that a pulse sequence and / or dynamic decoupling sequence are applied to the quantum memory unit to measure the decoherence rate of electron spins, and the measured decoherence rate of electron spins is less than 1 MHz. This feature advantageously achieves the measurement of even lower decoherence rates of electron spins.

[0073] According to the independent claim, the coupling rate of electron spins to spin bodies is greater than the decoherence rate of electron spins. As the decoherence rate of electron spins decreases, the number of detectable spin bodies increases for a given sample size, for example, in nanodiamonds. The number of detectable spin bodies for a given sample size corresponds to the number of spin bodies having a coupling rate greater than the decoherence rate of electron spins of the quantum emitter. Here, not only does the number of detectable spin bodies increase, but the quantum memory also has a longer lifetime because the decoherence rate is lower. In summary, this feature offers the advantage of being able to measure lower decoherence rates and, at the same time, making more spin bodies available for measurement.

[0074] Preferably, the coupling ratio of the electron spin of the quantum emitter to the spin of the spin body is less than 1 MHz. More preferably, the coupling ratio of the electron spin of the quantum emitter to the spin of the spin body is less than 1 kHz. Preferably, the spin body is the nuclear spin inside the nanodiamond.

[0075] The pulse sequence and / or dynamic decoupling sequence is preferably a Hahn echo sequence, a CPMG sequence, and / or an XY-N sequence. The CPMG sequence (Carr-Purcell-Meiboom-Gill sequence) is a method used in NMR spectroscopy and magnetic resonance imaging (MRI).

[0076] In another embodiment, the temperature of the nanodiamonds is above 100 mK. This feature is advantageous because it achieves less stringent cooling requirements compared to cooling to mK temperature. Preferably, the temperature of the nanodiamonds is above about 5 K. This feature is advantageous because it achieves even less stringent cooling requirements because liquid helium can be used to achieve this temperature range. Even more preferably, the temperature of the nanodiamonds is above about 70 K. This feature is advantageous because it achieves even less stringent cooling requirements because liquid nitrogen can be used to achieve this temperature range.

[0077] In yet another preferred embodiment, the quantum memory unit, in particular the electron spin and / or spin body of the quantum emitter, is designed and configured such that the quantum state of the spin body can be coherently manipulated and / or controlled by coherently controlling the electron spin of the quantum emitter and / or by applying microwave or RF radiation to the spin body.

[0078] This feature advantageously enables the quantum state of a spin body used for long-term storage of quantum information to transition to a predetermined state having arbitrary relative amplitude and relative phase.

[0079] When a spin body is a spin-1 / 2 particle or a two-level system, any state of the spin body corresponds to any point on the Bloch sphere.

[0080] The phrase "to manipulate coherently" means that the quantum state is altered in such a way that coherence is preserved.

[0081] According to the first alternative configuration, the quantum state of the spin body is coherently manipulated and / or controlled by coherently controlling the electron spin of the quantum emitter. This feature is made possible by the coupling between the electron spin of the quantum emitter and the spin body. As described above, the quantum emitter can communicate with flying Q-bits, and the spin body inside the nanodiamond is fairly well shielded from the environment other than the coupling to the quantum emitter. In other words, the electron spin of the quantum emitter can be said to act as a kind of intermediate, mediator, or broker between the flying Q-bits arriving from outside the nanodiamond and the spin body inside the nanodiamond.

[0082] The coupling between the electron spin of a quantum emitter and its spin body allows the quantum state of the spin body to be controlled by the state of the quantum emitter. The electron spin of the quantum emitter can be coherently manipulated and / or controlled using all-optical methods or microwave radiation. All-optical methods refer to techniques that use light for both input and output and do not require electronic data conversion. The use of all-optical methods or microwave radiation is a significant advantage because they are widely used and readily available methods. According to this method, the quantum state of the spin body is indirectly and coherently manipulated and / or controlled. This indirect drive has the advantage of allowing the spin body to be manipulated more quickly because the coupling of the electron spin to an external driving field is increased. For the same reason, an advantage here is that less driving force is required.

[0083] Another advantage is that electron spins can be decoupled during the operation of the spin body. This advantageously leads to improved decoherence of both the electron spins and the spin body.

[0084] The first alternative form can be realized by directing or irradiating light onto the quantum emitter. In this case, atomic transitions can be driven directly.

[0085] According to the second alternative form, the quantum state of the spin body is coherently manipulated and / or controlled by applying microwave or RF radiation to the spin body. In this case, the quantum state of the spin body is directly coherently manipulated and / or controlled.

[0086] Such direct manipulation has the advantage of allowing the electron spin of the quantum emitter to be controlled more independently of the manipulation of the spin body, thus reducing the impact on the quantum state of the spin body.

[0087] A further advantage of direct operation is that the drive sequence is generally simpler and requires fewer steps, making it easier to implement.

[0088] In a more preferred embodiment, the electron spin and spin body of the quantum emitter are designed and configured such that quantum information can be transferred from flying Q bits to the spin body and / or from the spin body to flying Q bits.

[0089] Here, when quantum information is transferred from a flying Q-bit to a spin body, this transfer is mediated by coupling between the electron spin of the quantum emitter and both the photons and spin body of the flying Q-bit. This also means that the electron spin of the quantum emitter and the spin body can become entangled.

[0090] This feature advantageously enables quantum information processing using a coherent light field without the need to transfer quantum information to a single photon state.

[0091] The transition of any entangled state of, for example, electron spin and spin body to a single-photon state has the advantage of being able to connect and / or entangle different quantum memory units, respectively. A single photon can be used as a mediator between two different quantum memory units.

[0092] According to another aspect of the present invention, the problem of the present invention is solved by the quantum register unit described in claim 14.

[0093] The quantum register unit includes a quantum memory unit as described above. However, the quantum memory unit includes a spin body inside or outside the nanodiamond, and the quantum register unit includes at least two spin bodies.

[0094] Furthermore, the electron spin of the quantum emitter is coupled to at least two spin bodies, where the at least two spin bodies are different spin bodies inside and / or outside the nanodiamond. Moreover, the coupling rate of the electron spin to each of the at least two spin bodies is greater than the decoherence rate of the electron spin. Each of the at least two spin bodies is designed and configured to be able to store quantum information internally, to be able to retrieve said quantum information, and / or to be able to manipulate the quantum state of said spin body.

[0095] A quantum register is understood to be a system containing at least two Q bits. This is a quantum analogue of a classical processor register. A quantum computer performs computations by manipulating the Q bits in a quantum register. A classical register with n bits can range from 0 to 2. n While a single value between -1 and -1 can be stored, a quantum register can simultaneously store a superposition of all these values.

[0096] This feature advantageously achieves the realization of quantum registers that can be used to implement quantum computing and quantum algorithms, quantum nodes, quantum networks and / or quantum communication systems.

[0097] Here, at least two spin bodies correspond to quantum registers.

[0098] By using the coupling between the electron spin of a quantum emitter and each of at least two spin bodies, all quantum states or a subset of all quantum states of a quantum register can be achieved.

[0099] According to one preferred embodiment of the quantum register unit, at least one of at least two spin bodies is coupled to at least one of at least two spin bodies, where the coupling rate between at least one of the at least two spin bodies and at least one of at least two spin bodies is greater than the maximum decoherence rate of the at least two spin bodies.

[0100] In the following, the phrase "at least two spin bodies" may alternatively be referred to as the total number of spin bodies, the phrase "at least one of the at least two spin bodies" may alternatively be referred to as the first number, and the phrase "at least one other of the at least two spin bodies" may alternatively be referred to as the second number.

[0101] If either the first or second number is greater than 2, the term "coupling rate" refers to at least two coupling rates. In this case, all coupling rates between the spin bodies of the first number and the spin bodies of the second number must be greater than the maximum decoherence rate of the total number of spin bodies.

[0102] The coupling between at least one of the total number of spin bodies and at least another of the total number of spin bodies favorably enables the exchange of quantum information between them. This means that at least one of the total number of spin bodies and at least another of the total number of spin bodies can become entangled.

[0103] The advantage of the embodiments described above is that the quantum states of at least two spin bodies can be manipulated more quickly and / or more directly by additional coupling or additional multiple couplings.

[0104] As described above, the spin body may be, or may include, the electron spin of an atom, the electron spin of a quantum emitter, in particular the electron spin of a color center or defect center and / or the nuclear spin of an atomic nucleus. According to a preferred embodiment of the quantum register unit, the spin body is the nuclear spin, in particular the nuclear spin of a carbon-13 isotope.

[0105] Embodiments of the present invention are shown in the drawings and will be described in more detail in the following description. [Brief explanation of the drawing]

[0106] [Figure 1] This is a schematic diagram showing a quantum memory unit according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing a SiV-center, which is a quantum emitter known in the relevant technical field. [Figure 3] This is a schematic diagram showing the SiV center used inside a nanodiamond, which is part of a quantum memory unit according to one embodiment of the present invention. [Figure 4] Figure 2 is a schematic diagram showing the electronic level structure of the SiV- center. [Figure 5] This figure shows the photoluminescence spectrum of the SiV-center of a nanodiamond known in the prior art. [Figure 6] This figure shows the photoluminescence spectrum of the SiV-center of a nanodiamond in a quantum memory unit according to one embodiment of the present invention. [Figure 7] This figure shows a partial level scheme for the transition C of the SiV-center of the nanodiamond in a quantum memory unit according to one embodiment of the present invention. [Figure 8] This figure shows the transitions C1, C2, C3, and C4 of the SiV-center transitions C of the nanodiamond in a quantum memory unit according to one embodiment of the present invention. [Figure 9]This is a schematic diagram showing a quantum memory unit with spin, according to one embodiment of the present invention, in which a spin body is located outside or on the surface of a nanodiamond. [Figure 10] Figure 3 shows the SiV-center and illustrates the relationship between flying photons, the electron spin of the SiV-center, and the nuclear spin of the spin body. [Figure 11] This figure shows a sample of nanodiamonds formed on a substrate. [Figure 12] This figure shows an experimental setup for realizing a quantum memory unit according to one embodiment of the present invention. [Figure 13] This figure shows an experimental setup for realizing a quantum memory unit according to one embodiment of the present invention. [Figure 14] This figure shows a pulse sequence used to measure specific parameters of a quantum memory unit according to one embodiment of the present invention. [Figure 15] This figure shows a coherent population trap (CPT) measurement of an SiV-center strongly coupled to the nuclear spin of one carbon-13 isotope to measure the coupling rate of electron spins to a spin body and the decoherence rate of electron spins, where the SiV-center is part of a nanodiamond quantum memory unit according to one embodiment of the present invention. [Figure 16] This figure illustrates a coherent population trap (CPT) measurement of an SiV-center coupled to two nuclear spins of two carbon-13 isotopes to measure the coupling rate and decoherence rate of the SiV-center's electron spins for each of three spin bodies, where the SiV-center and the three nuclear spins of the three carbon-13 isotopes are part of a quantum register unit according to one embodiment of the present invention. [Figure 17]This figure illustrates a coherent population trap (CPT) measurement of an SiV-center coupled to two nuclear spins of two carbon-13 isotopes to measure the coupling rate and decoherence rate of the SiV-center's electron spins for each of three spin bodies, where the SiV-center and the three nuclear spins of the three carbon-13 isotopes are part of a quantum register unit according to one embodiment of the present invention. [Figure 18] This is a schematic diagram showing a quantum register unit according to one embodiment of the present invention. [Figure 19] This figure shows yet another coherent population trap (CPT) measurement of an SiV-center, weakly coupled to the nuclear spin of one carbon-13 isotope, to measure the coupling rate of the electron spin to the spin body and the decoherence rate of the electron spin, where the SiV-center is part of a nanodiamond quantum memory unit according to one embodiment of the present invention. [Figure 20] This figure shows yet another coherent population trap (CPT) measurement of an SiV-center, weakly coupled to the nuclear spin of one carbon-13 isotope, to measure the coupling rate of the electron spin to the spin body and the decoherence rate of the electron spin, where the SiV-center is part of a nanodiamond quantum memory unit according to one embodiment of the present invention.

[0107] Figure 1 shows a negatively charged single silicon vacancy (SiV) as the quantum emitter 140. - A schematic diagram of a quantum memory unit 100 containing nanodiamonds 120 having a center 150 is shown.

[0108] SiV shown in Figure 2 - The center 150 is a quantum emitter 140 known in the art. This is a point defect in the lattice of a diamond crystal, in which one silicon atom Si is replaced by two carbon atoms C, where the silicon atom Si is located between two adjacent vacancies V, as shown in Figure 2.

[0109] SIV - The central atom 150 can be considered an artificial atom. SiV - The central 150 electron level structure is shown in Figure 4. SiV - The central level scheme of 150 includes four spin-degenerate orbital states, two of which form the ground state 200 and the excited state 210, respectively. The zero-phonon line (ZPL) between the ground state 200 and the excited state 210 has an energy of approximately 1.68 eV.

[0110] Both the ground state 200 and the excited state 210 exhibit level partitioning due to spin-orbit coupling. Therefore, both the ground state 200 and the excited state 210 have doublets separated by ΔGS and ΔES, respectively. The ground state partitioning ΔGS is approximately 46 GHz, and the excited state partitioning ΔES is approximately 252 GHz. The ground state 200 has a lower ground state 202 and an upper ground state 204. The lower ground state 202 and the upper ground state 204 are also called orbital ground states. The partition between the lower ground state 202 and the upper ground state 204 can also be called ground state partitioning or orbital ground state partitioning. The excited state 210 has a lower excited state 212 and an upper excited state 214. The lower excited state 212 and the upper excited state 214 are also called orbital excited states. The partition between the lower excited state 212 and the upper excited state 214 may be called an excited state partition or orbital excited state partition.

[0111] These level partitioning results in four photoactive transitions, which can be observed at extremely low temperatures. The inventors refer to these as transitions A, B, C, and D, and these are shown in Figure 5 as SiV with low strain. - This is shown for the center 150. Transition D is between the lower excited state 212 and the upper ground state 204, transition C is between the lower excited state 212 and the lower ground state 202, transition B is between the upper excited state 214 and the upper ground state 204, and transition A is between the upper excited state 214 and the lower ground state 202. SiV in low-strain nanodiamond 120 -When the center 150 is present, the wavelengths of transitions A, B, C, and D are 736 nm to 737 nm, with transition A having the shortest wavelength and transition D having the longest wavelength. The wavelength of transition C is approximately 736.75 nm.

[0112] The quantum memory unit 100 in the embodiment shown in Figure 1 is SiV - Including the center 150, the SiV - The center 150 is SiV in Figure 2 - Center 150 differs from the others in at least two features, as shown in Figure 3. Here, SiV - The electron spin of central 150 is coupled to a spin body 170 inside the nanodiamond 120. According to the embodiment of Figure 1, the spin body 170 is the nuclear spin of carbon-13 isotope 173, which is one of the carbon atoms C adjacent to one vacancy site V, as seen in Figures 1 and 3. The nuclear spin of carbon-13 isotope 173 is -1 / 2. SiV is shown in Figures 1 and 3. - The dashed line between the center 150 and carbon-13 isotope 173 represents SiV - This diagram illustrates the coupling between the center 150 and the spin body 170, i.e., carbon-13 isotope 173. Furthermore, the strain inside the nanodiamond 120 is large enough that the ground state resolution is on the order of 500 GHz, preferably 450-550 GHz. This strain inside the nanodiamond 120 is graphically represented in Figure 3 by the fact that the axis between two adjacent vacancy regions V, where silicon atoms Si are also located, is rotated, sheared, or tilted relative to the diagram in Figure 2.

[0113] SiV used in the mechanisms presented herein - The central 150 is located within the nanodiamond 120, which has a size of 20 nm to 1000 nm. The nanodiamond 120 is generated and coated onto the sapphire substrate 180 to ensure good thermal conductivity; see Figure 11 for details. The investigated SiV -Atomic force microscopy scans of nanodiamond 120, including the central 150, revealed nanodiamond 120 grain clusters with a size of approximately 600 nm. The SiV used in the experiments and measurements shown in Figures 12, 13, 15-17, 19, and 20. - The center 150 was located within this aggregate of nanodiamonds 120. Since the wavelengths of transitions C and D are in the 730-750 nm range, the size of nanodiamonds 120 in the embodiment of Figure 1 is smaller than the wavelength of the optical transitions of quantum emitter 140. The phonon wavelength of nanodiamonds 120 with a ground state resolution of 500 GHz is approximately 25 nm.

[0114] The SiV of Figure 2 has the atomic energy level structure of Figure 4. - The photoluminescence spectrum of the center 150 is shown in Figure 5. Individual color centers can be excited off-resonant using a continuous-wave 532 nm laser. In Figure 5, the intensity I as a function of the emission wavelength λ is shown in relative units. The four peaks correspond to the four transitions A, B, C, and D. The wavelength difference between transitions B and A and transitions D and C corresponds to ΔGS in Figure 4, and the wavelength difference between transitions C and A and transitions D and B corresponds to ΔES in Figure 4.

[0115] Figure 6 shows the SiV from Figure 3, which has increased strain inside nanodiamond 120. - The photoluminescence spectrum at the center 150 is shown. Similar to Figure 5, Figure 6 shows the intensity I as a function of the emission wavelength λ in relative units. Here, the ground state resolution ΔGS is approximately 510 GHz. Due to the high strain, the phonic process from the upper excited state 214 to the lower excited state 212 is faster than the optical lifetime, i.e., less than 1.7 ns. This makes transitions from the upper excited state 214 to the upper ground state 204, or from the upper excited state 214 to the lower ground state 202, less likely, and therefore characteristic lines A and B are hardly visible or not visible at all in the spectrum. Here, SiV with increased strain is shown. - If a central 150 is present, the wavelengths of transitions C and D are 730 nm to 750 nm.

[0116] SiV of quantum memory unit 100 - Since center 150 is coupled to the nuclear spin of carbon-13 isotope 173, the level scheme in Figure 4 needs to be modified as shown in Figure 7. Because the embodiments presented herein use only transition C, Figure 7 shows the spin levels of transition C.

[0117] By applying a magnetic field, the spin degeneracy of the ground state 200 and the excited state 210 can be relaxed. Four permanent magnets in a Halbach arrangement, which generate a magnetic field strength of approximately 400 mT inside a nanodiamond, are used to increase spin degeneracy.

[0118] On the left side of Figure 7, it is shown that transition C connects the low excited state level 212 to the low ground state level 202.

[0119] These two levels, namely 202 and 212, are split into two levels in a magnetic field by the known Zeeman effect. The split here is SiV - Electron spin at the center 150 and SiV - This is due to the spin-orbit interaction between the orbital states at the center of 150.

[0120] The low ground state 202 is divided into a spin-down state |↓> and a spin-up state |↑>, where spin is the electron spin of the quantum emitter. The low excited state 212 is divided into a spin-down state |↓'> and a spin-up state |↑'>.

[0121] The partition between the spin-down state |↓> and the spin-up state |↑> may be called the ground-state spin partition 220. The partition between the spin-down state |↓'> and the spin-up state |↑'> may be called the excited-state spin partition 222.

[0122] SIV -The electron spin of the central 150 is coupled to the nuclear spin of spin body 170, i.e., carbon-13 isotope 173, thereby splitting each of its energy levels into two separate states. Then, the electron spin of quantum emitter 140 is coupled with additional other spins to form a so-called composite spin. The nuclear spin is indicated by a double arrow symbol in Figure 7, where,

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[0123] Hyperfine levels

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[0124] Due to spin-orbit interaction, transitions A, B, C, and D are split into multiple lines. As in the embodiments presented herein, only transition C is used, and the splitting of transition C is shown in Figure 8. Transition C is split into four transitions C1, C2, C3, and C4. Transitions C2 and C3 are spin-conserving transitions. Transition C2 lies between the spin-down state |↓'> of the low excited state 212 and the spin-down state |↓> of the low ground state 202. Transition C3 lies between the spin-up state |↑'> of the low excited state 212 and the spin-up state |↑> of the low ground state 202. Transitions C1 and C4 are spin-flip transitions. Transition C1 lies between the spin-up state |↑'> of the low excited state 212 and the spin-down state |↓> of the low ground state 202. Transition C4 lies between the spin-down state |↓'> of the low excited state 212 and the spin-up state |↑> of the low ground state 202.

[0125] Quantum information can be stored in the spin bodies 170 within the nanodiamond 120 of the quantum memory unit 100, particularly in the carbon 13 isotope 173, as shown in Figure 7.

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[0126] The quantum memory unit 100 uses SiV for the nuclear spin of carbon-13 isotope 173. - The coupling ratio of the electron spin at the center 150 is greater than the electron spin decoherence ratio. This characteristic will be explained in relation to Figures 15 to 17.

[0127] Figure 9 shows schematic diagrams of different embodiments of the quantum memory unit 100 of Figure 1, where SiV - The central electron spin 150 is coupled to a spin body 170 located outside or on the surface of the nanodiamond 120. Here, spin body 170 is also the non-zero nuclear spin of carbon-13 isotope 173.

[0128] In another embodiment not shown herein, the electron spin of the quantum emitter 140 is coupled to a spin body 170 located inside the nanodiamond 120. The quantum memory unit 100 also has a second spin body outside the nanodiamond 120, and the electron spin of the quantum emitter 140 is coupled to the spin of this second spin body, where the coupling rate between the spin of spin body 170 and the electron spin of quantum emitter 140 is greater than the decoherence rate of the electron spin of quantum emitter 140. The coupling to the second spin body has the advantage that quantum information stored inside the nanodiamond can be coupled to an external quantum platform, such as superconducting technology, via the second spin body outside the nanodiamond 120, thereby forming interfaces between different processor units and / or memory units.

[0129] Figure 10 shows the SiV of the quantum memory unit 100. - The central 150, in particular, the electron spin, is shown to function as an intermediary or broker between the flying Q-bit 160 arriving from outside the nanodiamond 120 and the spin body 170 inside the nanodiamond 120. - The central electron spin 150 and the spin body 170 are designed and configured to transfer quantum information from the flying Q-bit 160 to the spin body 170, and then from the spin body 170 back to the flying Q-bit 160.

[0130] Figures 11-13 show experimental setups for realizing the quantum memory unit 100, particularly for measuring key features of the quantum memory unit 100, such as the coupling rate of electron spins to the spin body 170 and the decoherence rate of electron spins.

[0131] Nanodiamonds 120 are generated and coated onto a sapphire substrate 180 to ensure good thermal conductivity. See Figure 11 for details. The substrate 180 is placed in a continuous flow cryostat 320 and cooled to liquid helium temperature. The nanodiamonds 120 on the substrate 180 are investigated using a self-made confocal microscope. - Atomic force microscopy scans of nanodiamond 120, including the central 150, revealed the grain aggregates of nanodiamond 120.

[0132] The experimental setup shown in Figure 12 is described below.

[0133] A laser 340 is used to excite the nanodiamond 120 within the cryostat 320. For simplification, only one nanodiamond 120 is shown in Figures 12 and 13.

[0134] Laser 340 may be, for example, a Ti:sapphire laser capable of operating at 737 nm and tunable over a range beyond 80 nm. The laser linewidth is SiV - It is narrow enough to address the individual transitions of the central 150.

[0135] The laser beam emitted from laser 340 is modulated by modulator 342, which may be an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). Modulator 342 can be used to chop the signal from laser 340, thereby generating laser pulses of adjustable length. Alternatively, laser 340 can be used to form similarly adjustable sidebands with a desired frequency offset.

[0136] The modulated laser beam is reflected by mirror 356, passes through half-wave plate 362, and is then reflected by beam splitter cube 358 toward beam sampler 364. The beam sampler is an optical device that utilizes Fresnel reflection from an uncoated optical surface to extract a small proportion of the incident beam depending on the polarization state of the incident light. This is advantageous for applications where optical loss and wavefront distortion of the transmitted beam must be minimized. The laser beam reflected from beam sampler 364 is focused into objective lens 332 located in cryostat 320 using galvanoscanner 350 and two lenses 346. Nanodiamonds 120 can be exposed to microwave radiation using microwave source 344 fixed to substrate 180.

[0137] Light emitted from one nanodiamond 120 returns to the beam sampler 364 along the same path as the laser beam that excited the nanodiamond 120. Since the beam sampler 364 is transparent to the light emitted from the nanodiamond 120, the emitted light passes through the beam sampler 364, is reflected by another mirror 356, and is filtered by the long-pass filter 361. The long-pass filter 361 is essentially transparent to wavelengths longer than 750 nm, which is why, in terms of the setup here, it is SiV - The laser light used to excite the transition at the center 150 means that any laser light reflected by any optical element in the beam path does not pass through the long-pass filter 361 and does not interfere with subsequent measurements. The filtered light is then coupled to a single-mode fiber 369 using a fiber coupler 366. At the end of the single-mode fiber 369, the light is focused and detected by a single-photon counting module (SPCM) 368.

[0138] Figure 13 shows a plan view of the substrate 180 containing the nanodiamonds 120, as an enlarged view of the experimental setup shown inside circle 371 in Figure 12.

[0139] The nanodiamonds 120 are located on a substrate 180, on top of a microwave structure that includes a gold layer coated on the substrate 180. The microwave structure has a section 182 consisting of two large flat portions and a small strip-shaped section 184. The nanodiamonds 120 are located on the small strip-shaped portion 184. In this plan view of Figure 13, the substrate 180 is only visible in the black-colored smart section. The central conductor core of the coaxial cable connected to the microwave source 344 is connected to the strip-shaped section 184. The shield, i.e., ground, of the coaxial cable is connected to the two portions of section 182. The shape of the microstructure is formed so that microwave radiation is efficiently coupled into the interior of the nanodiamonds 120.

[0140] Figure 14 shows various methods or pulse sequences used to realize the quantum memory unit 100 or to measure important features of the quantum memory unit 100.

[0141] Figure 14 schematically shows four sequences 410, 412, 414, and 416 as a function of time t. Each box represents one element of the sequence described above. Boxes shown with solid lines are pulses or operations that use or include laser radiation. Boxes shown with dashed lines are pulses or operations that use or include microwave and / or RF radiation. Boxes shown with dashed lines represent waiting times.

[0142] Sequence 410 is a Rabi pulse sequence that can be used to determine the Rabi frequency for the transition used and the light field or light intensity used.

[0143] Sequence 412 is a Ramsey pulse sequence that can be used for measuring spin and decoherence time.

[0144] Sequences 414 and 416 are dynamic decoupling sequences known in the field of NMR that can be used to suppress decoherence. This means that when the decoherence rate of electron spin is measured using such dynamic decoupling sequences, the measured decoherence rate is smaller than the decoherence rate measured without such dynamic decoupling sequences.

[0145] Sequence 414 is a Hahn echo pulse sequence, sometimes referred to as a spin echo. Sequence 416 is an XY-N sequence.

[0146] According to the Rabi pulse sequence 410, first an initialization pulse 422 is applied to the quantum memory unit 100.

[0147] To do this, one of the spin cycle transitions, for example, the transition from the spin-down state |↓> of the low ground state 202 to the spin-down state |↓'> of the low excited state 212, is used so that the spin is reduced over a given time τ pump The low ground state 202 is optically pumped to a spin-up state |↑>. This is due to the fact that state |↓'> decays to a desired spin-up state |↑> with a low probability, and thereafter this desired spin-up state |↑> can no longer be driven by the laser. At the start of the measurement, the spins are distributed almost uniformly between the spin-up state |↑> and the spin-down state |↓>, i.e., 50% to 50% in thermal equilibrium. The spins are then pumped to a state with a specific probability, usually called fidelity, in this case the spin-up state |↑>. In the next step, a microwave pulse 423 is applied to the quantum memory unit 100. The fidelity here may be, for example, 90%.

[0148] The microwave pulse 423 has a duration τ ΜW It has a frequency ν ΜWIt resonates with the energy difference between the spin-up state |↑> and the spin-down state |↓>. In the case of free electron spin, this energy difference is equal to the so-called Zeeman splitting. Here, the microwaves are alternating in time magnetic field B MW (t) is the best case when the magnetic field is partially polarized so as to be orthogonal to the external DC magnetic field B0. MW When (t) is perpendicular to the external DC magnetic field B0, the intrinsic magnetic moment μ of the electron spin is S It becomes possible to couple to it. The relevant coupling strength Ω is the product of the driving magnetic field and the magnetic moment, i.e.

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[0149] In the next step, the spin state is read out using the same pulses that were used for initialization. This means that the read pulse 425 is the same as the initialization pulse 422.

[0150] This utilizes the fact that a resonant laser produces detectable fluorescence precisely when the corresponding state driven by the laser is occupied. In this case, fluorescence is high when the spin is in the spin-down state |↓>, which means that the laser is driving the transition from the spin-down state |↓> of the low ground state 202 to the spin-down state |↓'> of the low excited state 212.

[0151] The experiments here each involve different microwave durations τ ΜWIf repeated, the aforementioned oscillations can be measured so that the oscillation period of a single Rabi oscillation can be determined. In an exemplary measurement, the time it takes for the microwave to reverse the spin, i.e., the π pulse, was determined to be half of 609.4 ns. When the microwave duration is one-quarter of 609.4 ns, a superposition of the spin-up state |↑> and the spin-down state |↓> is prepared. The preparation of the superposition state is also visible on the equator of the Bloch sphere and forms the basis for the other pulse sequences in the figure here.

[0152] The Ramsay pulse sequence 412 begins with the same initialization pulse 422 as the Rabi pulse sequence 410. After step 422, the spin is in the spin-up state |↑> with the fidelity described above.

[0153] The next step 426 is a π / 2 pulse that generates a superposition of the spin-up state |↑> and the spin-down state |↓>. The decoherence is performed for a predetermined time τ Ramsey Measurement can be performed using a waiting step 428, which involves waiting only for a short time. For this purpose, another π / 2 pulse 426 is applied after the waiting step 428, and then in the readout step 425, the respective spin state populations are read out by the laser.

[0154] In the example measurement, bond strength

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[0155] Depending on the frequency and intensity of the spin noise, some of the noise can be decoupled from the signal using a special pulse sequence.

[0156] For this purpose, a π pulse with a variable microwave phase φ relative to the first π / 2 pulse is added between the first π / 2 pulse, which prepares the superposition, and the last π / 2 pulse, which converts the general state on the equator into a measurable spin population. This is called dynamic decoupling.

[0157] When there is only one π pulse, it is called a Hahn echo. Several π pulses with a relative phase of φ = π / 2 are called a CPMG.

[0158] When relative phases of 0 and π / 2 occur, these relative phases are often indexed with a subscript x or y, i.e., π x ,π y This sequence is called the XY-N sequence. The latter has the additional advantage of being able to correct the amplitude error of microwaves. The shorter the waiting time τ between two consecutive π pulses, the more high-frequency noise can be separated.

[0159] The Hahn echo pulse sequence 414 begins with the same initialization pulse 422 as the Rabi pulse sequence 410. After step 422, the spin is in the spin-up state |↑> with the fidelity described above. In the next step 426, a π / 2 pulse is applied so that the spin state is located on the equator of the Bloch sphere. The next step 428 is a wait pulse that waits for a given time τ. During this time, different realizations of the same quantum state proceed randomly by picking up noise from the environment. The next step 432 is a π pulse, which rotates the Bloch sphere 180° around the horizontal axis so that the relative population remains invariant and the relative phase takes on a negative sign. The following step is a wait pulse 428 that waits for a given time τ, as described above. Here, different relative phases are picked up randomly during the wait pulse, which is the same as in the first wait pulse 428 so that ideally all phase sums cancel each other out, as described above. The next step, 426, is another π / 2 pulse, which rotates the Bloch sphere back to its starting pole, each of which is a different realization under ideal conditions. In the final steps 422 and 425, the spin state is read out.

[0160] In exemplary measurements of the Hahn echo pulse sequence 414, a coherence time of 42 μs was measured, which is significantly longer than the 3 μs coherence time measured using the Ramsay pulse sequence 412 described above.

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[0161] The XY-N sequence 416 begins with the same initialization pulse 422 as the Rabi pulse sequence 410. After step 422, the spin is in the spin-up state |↑> with the fidelity described above. The following step 434 is π y / 2 pulse, that is, a π / 2 pulse centered on the y-axis of the Bloch sphere. The next step 430 is a pulse sequence consisting of N sequences, this sequence is the next step, i.e., waiting time τ,π x Pulse, waiting time 2·τ,π y Pulse, waiting time 2·τ,π x Pulse, waiting time 2·τ,π y Pulse, waiting time 2·τ,π y Pulse, waiting time 2·τ,π x Pulse, waiting time 2·τ,τ y Pulse, waiting time 2·τ,π x The pulse and waiting time τ are included in this order. In the next step 436, 3 / 2·π y A pulse is applied. The XY-N sequence 416 is alternatively an 8π pulse, i.e., 4π. x and 4π y Because it includes pulses, it can be called an XY8-N sequence. In the next final steps 422 and 425, the spin state is read out.

[0162] Exemplary measurements of the XY-N sequence 416 were also performed with the current setup. Here, the coherence time was measured to be approximately 100 μs.

[0163] The illustrative measurements here demonstrate resonance. These resonances result from the rotation of the nucleus due to coupling to electron spins that are repeatedly flipped by π pulses. Here, once the electron spins are initially prepared in a predetermined state, the nucleus can be rotated to any state using a sequence of quantum operations on the electrons. In particular, a special sequence of quantum operations can be used to "swap" the electron spin state to the nucleus. That is, the quantum state of the electron spin after the swap becomes the quantum state of the nucleus spin before the swap, and the quantum state of the nucleus spin after the swap becomes the quantum state of the electron spin before the swap.

[0164] Indirect manipulation of nuclear spin here via electron spin, for example, initially brings the nuclear spin up state

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[0165] In an exemplary measurement of Rabi oscillations of nuclear spin, the nuclear spin is first indirectly initialized, then rotated, and finally read out. Approximately 160π pulses were captured for the electron spin relative to the nuclear spin, and it was observed that it oscillated completely into Rabi oscillations. This is because approximately 40π pulses were captured for the electron spin, resulting in a nuclear spin-up state.

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[0166] Figure 15 shows one SiV strongly coupled to one nuclear spin of carbon-13 isotope 173. - Coherent population trap (CPT) measurements at center 150 are shown. The objective of this experiment was to measure the decoherence rate of electron spin or spin coherence time T2. SiV under investigation - The central 150 was part of the aforementioned granular mass.

[0167] A coherent population trap (CPT) is used to inspect or measure spin coherence. For this purpose, a laser resonantly drives a spin-flip transition, i.e., transition C1 or C4 shown in Figure 8. Simultaneously, an electro-optic modulator (EOM) 342 forms a sideband over which a sweep should be performed across the corresponding spin-conserving transition, i.e., transition C2 or C3. Once the Raman condition is met, the system is pumped into a dark state to extinguish the fluorescence signal. Figure 15 shows the fluorescence signal 510 from a CPT measurement. The fluorescence signal 510 shows an intensity signal I in arbitrary units, normalized to the maximum intensity. The fluorescence signal 510 has measurement points reproduced as dots. The curve was fitted to the measurement points using a triple Lorentz fitting function. The fluorescence signal 510 is plotted against the frequency difference between the frequency of the formed sideband and the frequency of the laser with a given offset. In this case, the offset is shown in the lower right corner of Figure 15. The offset is 10995.4 MHz. SiV under consideration - Regarding the center 150, two dropouts 512 and 514 occurred with a frequency division of A = (38.47 ± 0.12) MHz. The division is

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[0168] The two depressors are formed as follows: transition C4 is always driven, and one sideband formed by the electro-optic modulator (EOM) 342 is swept across transition C2. Due to the nuclear spins near carbon-13 isotope 173, two independent lambda (Λ) schemes arise, each forming a typical coherent population trap (CPT) depressor. The first lambda (Λ) scheme is,

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[0169] Furthermore, since the linewidth of the degraded portion provides insight into the spin decoherence rate, power-dependent measurements were performed. By fitting the data to a Lorenzian and extracting the linewidth Γ2, the decoherence rate could be linearly extrapolated to zero laser power, eliminating the power-induced broadening. As a result, a zero-power linewidth of Γ2 = (320 ± 120) kHz was obtained. This is equal to a spin coherence time T2 of approximately 0.5 μs. This represents a decoherence rate reduced by approximately 10 times compared to previously reported measurements in bulk diamond at comparable temperatures. Considering the latter improvement in spin coherence in high-strain environments, a spin transition frequency of approximately 11 GHz and a spin cyclic transition division of 390 MHz are relatively high-strain SiV - This suggests that a GS division on the order of 500 GHz occurred as a result.

[0170] In this embodiment, the coupling ratio between the electron spin and spin body A is approximately 120 times greater than the decoherence rate Γ2 of the electron spin.

[0171] Next, the spin environment in the same aggregate of nanodiamond 120 is examined using different SiV - Further investigation was conducted by performing additional CPT measurements on the central 150.

[0172] Figure 16 shows another coherent population trap (CPT) measurement performed in a similar manner to the measurement shown in Figure 15.

[0173] The fluorescence signal 520 shows an intensity signal I in arbitrary units, normalized to the maximum intensity. The fluorescence signal 520 is plotted against the frequency difference between the frequency of the formed sideband and the frequency of the laser with a given offset. In contrast to the embodiment in Figure 15, the offset shown in the lower right corner of Figure 16 is 10782.6 MHz.

[0174] The fluorescence signal 520 in Figure 16 shows two attenuations 521 and 522 separated by A = (41.5 ± 0.7) MHz. Measurement of attenuation 522 at reduced power yielded two further attenuations 523 and 524 separated by A' = (5.47 ± 0.17) MHz, as shown in Figure 17. The values ​​of the reduced power measurements shown in Figure 17 correspond to the portion of Figure 16 indicated by the dashed-dotted frame 525. Attenuation 523 has a linewidth of (3.2 ± 0.4) MHz, and attenuation 524 has a linewidth of (4.3 ± 0.5) MHz. Attenuation 521 was also measured at low power, where two further attenuations were resolved, but these are not reproduced here.

[0175] This means that two spin bodies are coupled to the quantum emitter 140. For example, one spin body can be coupled with the first spin body at a coupling rate of approximately 44.2 MHz, and the other spin body can be coupled with the first spin body at a coupling rate of approximately 38.8 MHz.

[0176] Alternatively, one spin body can be coupled with the first spin body at a coupling rate of approximately 41.5 MHz, and the other spin body can be coupled with the first spin body at a coupling rate of approximately 5.47 MHz.

[0177] Different line widths generally result in only moderate distortion and each has different coherence characteristics, as seen in the surrounding SiV. -This suggests coupling to two other electron spins at the center 150. Assuming that the electron-electron bonding of the dipole corresponds to distances on the order of a few nanometers, the size of the nanodiamond 120 being studied and SiV - This is reasonable for the density of the central 150.

[0178] The measurements here indicate that the system measured in Figures 16 and 17 is the quantum register unit 300. This is because SiV - This is because the central electron spin of 150 is coupled to two non-zero spin bodies, which are the nuclear spins of two carbon-13 isotope 173 inside the nanodiamond 120.

[0179] Figure 18 shows one embodiment of the quantum register unit 300. The first spin body 181, which is a carbon-13 isotope, is SiV - While strongly coupled to the central 150 electron spin, SiV - The coupling between the second spin body 182 and the third spin body 183 to the central electron spin 150 is weak. Furthermore, the coupling between the three spin bodies 181, 182, and 183 is also weak, as indicated by the low amplitude of the curves connecting the three spin bodies 181, 182, and 183 to each other. Quantum information can be stored using each of the spin bodies 181, 182, and 183, and this quantum information can be retrieved from it, and the quantum state of the spin bodies can also be manipulated.

[0180] Furthermore, using the flying Qbit 160, the quantum information of the flying Qbit 160 is stored in the SiV of the quantum register unit 300. - It can be exchanged with center 150. The meaning of the term "exchanged quantum information" can include the transfer and retrieval of quantum information. In this case, the SiV of quantum register unit 300. - The quantum information of the central 150 can be exchanged with one of the three non-zero spin bodies 181, 182, and 183.

[0181] Here, similar to the embodiment described above in Figure 15, the electron spin coupling ratio A, which is 5.2 MHz in this case, is greater than the electron spin decoherence ratio, which is approximately 2.2 MHz in this case.

[0182] Figure 19 shows another coherent population trap (CPT) measurement performed in a similar manner to the measurements shown in Figures 15-17.

[0183] The fluorescence signal 530 shows an intensity signal I in arbitrary units, normalized to the maximum intensity. The fluorescence signal 530 is plotted against the frequency difference between the frequency of the formed sideband and the frequency of the laser with a given offset. In contrast to the embodiment described in the previous figure, the offset shown in the lower right corner of Figure 19 is 10896.8 MHz.

[0184] The fluorescence signal 530 in Figure 19 is one SiV - This indicates that the center 150 is coupled to one nuclear spin of carbon-13 isotope 173. The fluorescence signal 530 in Figure 19 shows a single decoherence 531. Measurement of decoherence 531 with reduced power yielded two further decoherences 532, 534, separated by A = (5.20 ± 0.14) MHz, as shown in Figure 20. The reduced power measurements shown in Figure 20 correspond to the portion of Figure 19 shown by the dashed-dotted frame 535. Decoherence 532 has a linewidth of (2.0 ± 0.3) MHz, and decoherence 534 has a linewidth of (2.6 ± 0.5) MHz. The linewidths of decoherences 532 and 534 are aligned within their respective error bars and correspond to the decoherence rates of the electron spins.

[0185] SiV of the embodiments shown in Figures 16 and 17, each having a different line width. - In contrast to the multi-lowered structure of the central 150, the SiV of the present invention -The fact that the central 150 is tightly matched and has a relatively narrow linewidth indicates weakly coupled neighboring carbon-13 nucleus spins with a coupling strength of 5.2 MHz. In this case, the distance between the two coupled spins is on the order of 1 Å.

[0186] Here, similar to the embodiment described above in Figure 15, the electron spin coupling ratio A, which is 5.2 MHz in this case, is greater than the electron spin decoherence ratio, which is approximately 2.2 MHz in this case.

Claims

1. A quantum memory unit (100), It contains nanodiamonds (120) having quantum emitters (140), The electron spin of the quantum emitter (140) is coupled to a spin body (170) inside or outside the nanodiamond (120), The coupling rate of the electron spin to the spin body (170) is greater than the decoherence rate of the electron spin, and The spin body (170) It is possible to store quantum information internally and to retrieve said quantum information from there, and / or The quantum state of the spin body (170) can be manipulated. Designed and configured, Quantum memory unit (100).

2. The spin body (170) is a non-zero nuclear spin or electron spin body of an atom (173). The quantum memory unit (100) according to claim 1.

3. The quantum memory unit (100) according to claim 2, wherein the atom (173) is a carbon-13 isotope, a Si-29 isotope, an N-15 isotope, or an atom (173) inside or outside a nanodiamond (120) having a non-zero nuclear spin.

4. The internal strain of the nanodiamond (120) is greater than a predetermined value such that the ground state resolution is greater than 46 GHz, preferably greater than 0.5 THz. A quantum memory unit (100) according to any one of claims 1 to 3.

5. The size of the nanodiamond (120) is smaller than the wavelength of the optical transition of the quantum emitter (140) in the nanodiamond (120) and / or smaller than the wavelength of the phonon in the nanodiamond (120) corresponding to the energy of the ground state division. A quantum memory unit (100) according to any one of claims 1 to 4.

6. The quantum emitter (140) is a color center of group IV, preferably a single negatively charged silicon vacancy (SiV). － The center (150) A quantum memory unit (100) according to any one of claims 1 to 5.

7. The quantum memory unit (100) further, The nanodiamond (120) includes a second spin body outside the nanodiamond (120), the electron spin of the quantum emitter (140) is coupled to the spin of the second spin body, and the coupling ratio of the spin of the spin body (170) to the electron spin of the quantum emitter (140) is greater than the decoherence rate of the electron spin of the quantum emitter (140). A quantum memory unit (100) according to any one of claims 1 to 6.

8. The quantum memory unit (100) according to any one of claims 1 to 7, wherein the coupling rate of the electron spin to the spin body (170) is greater than 0.01 MHz, preferably greater than 5 MHz.

9. The quantum memory unit (100) according to any one of claims 1 to 8, wherein the decoherence rate of the electron spin is smaller than the electron spin flip rate during operation.

10. The quantum memory unit (100) is To measure the decoherence rate of the electron spin, a pulse sequence and / or a dynamic decoupling sequence, preferably a Hahn echo sequence, a CPMG sequence and / or an XY-N sequence, is applied to the quantum memory unit (100), and The measured decoherence rate of the electron spin is less than 1 MHz, Designed and constructed A quantum memory unit (100) according to any one of claims 1 to 9.

11. The quantum memory unit (100) according to any one of claims 1 to 10, wherein the temperature of the nanodiamond (120) is greater than about 100 mK, preferably greater than about 5 K, and more preferably greater than about 70 K.

12. The quantum memory unit (100), in particular the electron spin of the quantum emitter (140) and / or the spin body (170), By coherently controlling the electron spin of the quantum emitter (140), and / or By applying microwaves or high frequencies to the spin body (170), The quantum state of the spin body (170) is coherently operable and / or controllable. Designed and configured in such a way, A quantum memory unit (100) according to any one of claims 1 to 11.

13. The electron spin of the quantum emitter (140) and the spin body (170) are designed and configured such that quantum information can be transferred from the flying Q-bit (160) to the spin body (170) and / or from the spin body (170) to the flying Q-bit (160). A quantum memory unit (100) according to any one of claims 1 to 12.

14. A quantum register unit (300) including a quantum memory unit according to any one of claims 1 to 13, The electron spin of the quantum emitter (140) is coupled to at least two spin bodies (181, 182, 183), The at least two spin bodies (181, 182, 183) are different spin bodies located inside and / or outside the nanodiamond (120), The coupling ratio of the electron spins for each of the at least two spin bodies (181, 182, 183) is greater than the decoherence rate of the electron spins. Each of the at least two spin bodies (181, 182, 183) is designed and configured to be able to store quantum information internally, to be able to retrieve said quantum information, and / or to be able to manipulate the quantum state of said spin body. A quantum register unit (300) characterized by the above.

15. At least one of the at least two spin bodies (181, 182, 183) is coupled to at least one other spin body (181, 182, 183) from the at least two spin bodies (181, 182, 183), The coupling ratio between at least one spin body (181, 182, 183) of the at least two spin bodies (181, 182, 183) and at least one other spin body (181, 182, 183) of the at least two spin bodies (181, 182, 183) is greater than the maximum decoherence ratio of the at least two spin bodies (181, 182, 183). The quantum register unit (300) according to claim 14.

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