Quantum state preparation method and apparatus

Abstract

Disclosed are a quantum state preparation method and apparatus, which belong to the field of quantum computing. The method comprises: using different spin states as targets, and sequentially performing two instances of quantum state preparation on a harmonic oscillator; performing spin state detection on a spin state corresponding to the harmonic oscillator; and when the spin state does not meet a condition, repeating the quantum state preparation and the spin state detection until the spin state meets the condition, so as to obtain a harmonic oscillator of a target quantum state. By means of a cyclic process involving quantum state preparation and spin state detection, it is ensured that a harmonic oscillator is finally prepared into a target quantum state, thereby ensuring the preparation effect.

Description

Quantum state preparation method and device

[0001] This application claims priority to Chinese patent application No. 202410212778.2, filed on February 26, 2024, entitled “Quantum State Preparation Method and Apparatus,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of quantum computing, and in particular to a method and device for preparing a quantum state. Background Art

[0003] Trapping ions in an ion trap forms an oscillator, which can be used for quantum computing. Before using the oscillator for quantum computing, it is usually necessary to prepare the oscillator's quantum state to the ground state through quantum state preparation.

[0004] In the related art, the method for preparing the quantum state is as follows: by applying a suitable laser to excite the sideband resonant transition, the oscillator is caused to transition from a higher vibration quantum number to a lower vibration quantum number, and the quantum state of the oscillator is cooled to the ground state.

[0005] However, the above method requires frequency resolution of the vibration mode of the oscillator and then targeted application of appropriate laser light. This method is difficult to ensure the quantum state preparation effect of the oscillator when the vibration mode discrimination of the oscillator is low. Summary of the Invention

[0006] The present application provides a quantum state preparation method and device, which can ensure the quantum state preparation effect of a resonator.

[0007] In a first aspect, the present application provides a method for preparing a quantum state. The method comprises: sequentially preparing a quantum state of a resonator twice using different spin states as targets; performing spin state detection on the spin state corresponding to the resonator; and, if the spin state does not meet a condition, repeating the quantum state preparation and spin state detection until the spin state meets the condition, thereby obtaining a resonator in the target quantum state.

[0008] Among them, the oscillator is the external state of the ion, and the spin state corresponding to the oscillator is also the spin state of the ion corresponding to the oscillator, that is, the internal state of the ion.

[0009] In this implementation, when the oscillator is subjected to quantum state preparation, since it is impossible to ensure that the external state can be prepared to the ground state, but it is possible to ensure that the internal state (spin state) corresponding to the prepared oscillator is obtained, two quantum state preparation operations are performed with different spin states as targets. Since the spin state corresponding to the oscillator that has reached the ground state does not change, the spin state after the quantum state preparation is detected. If the conditions are not met, it indicates that the oscillator has not yet reached the ground state. The quantum state preparation is repeated until the spin state after the quantum state preparation is detected meets the conditions, indicating that the oscillator is in the target quantum state (the external state is the ground state). Through the cyclic process of quantum state preparation and spin state detection, it is ensured that the oscillator is eventually prepared to the target quantum state, thereby ensuring the preparation effect.

[0010] In an implementation of the present application, the spin state meeting the condition includes: the spin state has not changed since the last quantum state preparation. Correspondingly, the spin state not meeting the condition includes: the spin state has changed since the last quantum state preparation.

[0011] For example, two quantum state preparations target the first and second spin states, respectively. After the first quantum state preparation, the spin state is the first spin state. At this point, the external state of the oscillator may or may not be the ground state. If it is the ground state, the second quantum state preparation cannot change the spin state, that is, the spin state remains in the first spin state, and the spin state condition is met. If it is not the ground state, the second quantum state preparation can change the spin state, that is, the spin state becomes the second spin state, and the spin state condition is not met.

[0012] For example, a first spin state is used as a target, and quantum state preparation is performed on the oscillator to obtain a oscillator corresponding to the first spin state; a second spin state is used as a target, and quantum state preparation is performed on the oscillator; a spin state detection is performed on the spin state corresponding to the oscillator; when the spin state is the second spin state, the quantum state preparation and spin state detection are repeated until the spin state is the first spin state, thereby obtaining a oscillator in the target quantum state. When the spin state is the first spin state, it indicates that the oscillator in the target quantum state has been obtained, and the quantum state preparation and spin state detection are no longer necessary.

[0013] In some possible implementations of the present application, the quantum state preparation adopts one of the following methods: sideband cooling technology and rapid adiabatic channel technology. The above technologies can realize quantum state preparation with the goal of setting the spin state.

[0014] Quantum state preparation refers to the use of the above-mentioned technology to process the ions corresponding to the oscillator, thereby achieving quantum state manipulation of the oscillator. The use of sideband cooling technology or rapid adiabatic channel technology can prepare the internal state of the ion to a set spin state, which is not described in detail in this application.

[0015] In some other possible implementations of the present application, the quantum state preparation may also adopt other cooling technologies.

[0016] In some possible implementations of the present application, detecting the spin state corresponding to the oscillator includes detecting the spin state corresponding to the oscillator using a state-dependent fluorescence detection technique. Using the state-dependent fluorescence detection technique enables rapid and accurate measurement of the spin state.

[0017] In some other possible implementations of the present application, other detection technologies may also be used to detect the spin state.

[0018] In some possible implementations of the present application, the target quantum state is a ground state, the first spin state is |↑>, and the second spin state is |↓>.

[0019] In some other possible implementations of the present application, the target quantum state is a ground state, the first spin state is |↓>, and the second spin state is |↑>.

[0020] In some possible implementations of the present application, the repeating of the quantum state preparation includes:

[0021] In each cycle, the first spin state and the second spin state are sequentially used as targets to perform two quantum state preparations on the oscillator.

[0022] In this implementation, the quantum state preparation is repeated twice each time, and then a spin state detection is performed (it is assumed that the first quantum state preparation reaches the first spin state) to determine whether the spin state changes after the second quantum state preparation, thereby determining whether the ground state oscillator is obtained.

[0023] In some other possible implementations of the present application, the repeating of the quantum state preparation includes:

[0024] In odd cycles, the first spin state is used as a target to prepare the quantum state of the oscillator; in even cycles, the second spin state is used as a target to prepare the quantum state of the oscillator.

[0025] For example, a first spin state is used as a target, and a quantum state preparation is performed on the oscillator. Then, a spin state detection is performed on the spin state corresponding to the oscillator. If the spin state is the second spin state, the oscillator in the target quantum state is obtained. If the spin state is the first spin state, a second spin state is used as a target, and a quantum state preparation is performed on the oscillator. Then, a spin state detection is performed on the spin state corresponding to the oscillator. If the spin state is the first spin state, the oscillator in the target quantum state is obtained. Otherwise, the above process is repeated.

[0026] Optionally, before preparing the quantum state of the oscillator, the method further includes obtaining the oscillator.

[0027] In some examples, a method for obtaining a resonator is as follows: trapping N ions to obtain 3N resonators, where N is a positive integer; and obtaining M resonators from the 3N resonators based on a quantum information processing task, where M is a positive integer less than 3N.

[0028] The M resonators may be selected randomly or in other ways, which is not limited.

[0029] In this implementation, N ions can form a long chain with 3N vibration modes, thereby obtaining 3N oscillators, and the oscillators for quantum state preparation can be obtained from the prepared 3N oscillators.

[0030] In other examples, the ions may also form other structures, which are not limited in this application.

[0031] In the implementation of the present application, the M oscillators are each prepared for quantum state through M cycles. That is, each oscillator is prepared to the target quantum state according to the above method, and then the quantum state of another oscillator is prepared.

[0032] In a second aspect, the present application provides a quantum state preparation device, the device comprising:

[0033] A quantum state preparation unit is used to sequentially perform two quantum state preparations on the oscillator using different spin states as targets;

[0034] A detection unit, configured to perform spin state detection on the spin state corresponding to the resonator;

[0035] A control unit is used to control the quantum state preparation unit and the detection unit to repeat the quantum state preparation and the spin state detection when the spin state does not meet the conditions, until the spin state meets the conditions, thereby obtaining a resonator of the target quantum state.

[0036] Optionally, the spin state satisfies a condition including:

[0037] The spin state has not changed after the last quantum state preparation.

[0038] Optionally, the target quantum state is obtained by using a first spin state as a target to prepare the quantum state of the oscillator, thereby obtaining a oscillator corresponding to the first spin state; and using a second spin state as a target to prepare the quantum state of the oscillator.

[0039] The control unit is used to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

[0040] Optionally, the target quantum state is obtained by using a first spin state as a target to prepare the quantum state of the oscillator, thereby obtaining a oscillator corresponding to the first spin state; and using a second spin state as a target to prepare the quantum state of the oscillator.

[0041] The control unit is used to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

[0042] Optionally, the device further comprises:

[0043] The ion trapping unit is used to trap N ions to obtain 3N resonators, where N is a positive integer;

[0044] An acquisition unit is used to acquire M resonators from the 3N resonators based on a quantum information processing task, where M is a positive integer less than 3N.

[0045] Optionally, the M oscillators prepare quantum states respectively through M cycles.

[0046] In a third aspect, an electronic device is provided, which is the aforementioned quantum state preparation device.

[0047] The electronic device includes a processor and a memory. The memory is used to store software programs and modules. The processor implements the method of the first aspect or any possible implementation of the first aspect by running or executing the software programs and / or modules stored in the memory.

[0048] Optionally, there are one or more processors and one or more memories.

[0049] Optionally, the memory may be integrated with the processor, or the memory may be provided separately from the processor.

[0050] In the specific implementation process, the memory can be a non-transitory memory, such as a read-only memory (ROM), which can be integrated on the same chip as the processor or be set on different chips. This application does not limit the type of memory and the setting method of the memory and the processor.

[0051] In a fourth aspect, a computer program product is provided, wherein the computer program product includes computer program code, and when the computer program code is executed by a computer, the computer executes the method in the first aspect or any possible implementation of the first aspect.

[0052] In a fifth aspect, the present application provides a computer-readable storage medium, which is used to store program codes executed by a processor, wherein the program codes include methods for implementing any possible implementation of the first aspect.

[0053] In a sixth aspect, a chip is provided, comprising a processor, the processor being configured to call and execute instructions stored in a memory from the memory, so that an electronic device equipped with the chip executes a method in any possible implementation of the first aspect above.

[0054] In a seventh aspect, another chip is provided. The chip includes an input interface, an output interface, a processor, and a memory. The input interface, the output interface, the processor, and the memory are connected via an internal connection path. The processor is configured to execute code in the memory. When the code is executed, the processor is configured to perform the method in any possible implementation of the first aspect.

[0055] In an eighth aspect, a quantum computing system is provided, which includes a quantum state preparation device as in the second aspect or any possible embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG1 is a schematic diagram of an electrode of an ion trap provided in an embodiment of the present application;

[0057] FIG2 is a schematic diagram of a quantum state provided in an embodiment of the present application;

[0058] FIG3 is a flow chart of a quantum state preparation method provided in an embodiment of the present application;

[0059] FIG4 is a schematic diagram of a quantum state change during a second quantum state preparation according to an embodiment of the present application;

[0060] FIG5 is a flow chart of a quantum state preparation method provided in an embodiment of the present application;

[0061] FIG6 is a schematic diagram of a sideband Rabi frequency and detuning amount scanning waveform in the fast adiabatic channel technology provided by an embodiment of the present application;

[0062] FIG7 is a schematic diagram of simulation results of quantum state preparation using the method of the present application provided in an embodiment of the present application;

[0063] FIG8 is a flow chart of a quantum state preparation method provided in an embodiment of the present application;

[0064] FIG9 is a block diagram of a quantum state preparation device provided in an embodiment of the present application;

[0065] FIG10 is a schematic structural diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0066] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0067] For ease of understanding, the following examples provide some explanations of concepts related to the embodiments of the present application for reference.

[0068] (1) Energy level

[0069] Energy level theory explains the orbits of electrons outside the atomic nucleus. It posits that electrons can only move in specific, discrete orbits, each with its own distinct energy, known as an energy level. In other words, each specific energy state of an electron in an atom is called an energy level. Energy levels can also be called "energy states."

[0070] (2) Ground state and excited state

[0071] Under normal conditions, the electrons in an atom move only in the lowest energy level closest to the nucleus. This state of motion is called the ground state of the atom. The excited state is when electrons in an atom receive energy and jump from a lower energy level to a higher energy level. This higher energy state is called an excited state.

[0072] (3) Transition

[0073] A quantum transition is a process in which the state of a quantum mechanical system undergoes a sudden change. The process by which atoms, under the irradiation of light, jump from a high (low) energy state to a low (high) energy state by emitting (absorbing) photons is a typical quantum transition. Even without light, atoms in an excited state can transition to a lower energy state and emit photons (spontaneous emission) under the influence of zero-field fluctuations in a vacuum. In addition to radiation processes, other processes such as scattering and decay are also considered quantum transitions. Furthermore, the wavelength of light that causes an atom or ion to undergo a quantum transition is called its transition wavelength.

[0074] Quantum transitions are probabilistic processes, a fundamental characteristic of quantum laws. For example, when an atomic energy level transition occurs, it's impossible to predict when a particular atom will make the transition. Some transitions may occur earlier than others, while others may occur later. Therefore, the lifetime of an atom in an excited state is not uniform. However, for a large number of atoms, the average lifetime of the excited state is certain and can be measured experimentally and calculated theoretically.

[0075] (4) Resonator

[0076] As shown in Figure 1, an ion trap applies electrical signals (typically radio frequency (RF) and direct current (DC)) to electrodes, confining charged ions in space to form an ionic crystal (which can be arranged in a one-dimensional chain, a two-dimensional plane, or a three-dimensional structure). These charged ions interact with each other through Coulomb forces and oscillate rapidly in space, forming multiple vibration modes. A long chain of N ions has 3N vibration modes, each of which is a resonator, or phonon.

[0077] Typically, an ion trap consists of a control system, a trapping electromagnetic field generator and trapping electrodes, a laser system, a vacuum system, and a detection system. The control system generates timing and switches, while the laser system includes ionizing light, cooling light, pump light, control light, and detection light.

[0078] The application scenario of this application is to trap multiple ions (generally arranged with a spacing of micrometers) and use lasers to prepare specific quantum states. By introducing the new quantum state preparation method proposed in this application, the fidelity of quantum state preparation can be greatly improved.

[0079] (5) Quantum state

[0080] The quantum state includes the internal state and the external state. Figure 2 is a schematic diagram of a quantum state, as shown in Figure 2, where the dotted box on the left represents the internal state, also known as the spin state including |↑> and |↓>, with a total of N (N ions); the dotted box on the right represents the external state, that is, the aforementioned oscillator, with a total of M (M oscillators selected from 3N). The oscillator itself is a structure with infinite energy levels, which are arranged according to the energy size from |0>, |1>, |2>..., and these energy levels are generally equidistant. In the figure above, represents the direct product, indicating the coupling between internal states, between external states, and between internal and external states.

[0081] (6) Cooling

[0082] Before manipulating and detecting ions in an ion trap, cooling is required to lower the oscillator to its ground state, the energy level |0>. Cooling methods include sideband cooling, rapid adiabatic channel cooling, cooperative cooling, and Doppler cooling.

[0083] FIG3 is a flow chart of a quantum state preparation method provided in an embodiment of the present application. As shown in FIG3 , the method includes the following steps.

[0084] S101: Using different spin states as targets, perform two quantum state preparations on the oscillator in sequence.

[0085] Here, different spin states refer to |↑> and |↓> respectively.

[0086] S102: Performing spin state detection on the spin state corresponding to the resonator.

[0087] Step S102 detects the spin state after the second quantum state preparation.

[0088] S103: When the spin state does not satisfy the condition, repeat the quantum state preparation and the spin state detection until the spin state satisfies the condition, thereby obtaining a resonator of a target quantum state.

[0089] In an implementation of the present application, the spin state meeting the condition includes: the spin state has not changed since the last quantum state preparation. Correspondingly, the spin state not meeting the condition includes: the spin state has changed since the last quantum state preparation.

[0090] For example, the two quantum state preparations target the first spin state and the second spin state respectively. After the first quantum state preparation, the spin state is the first spin state. At this time, the external state of the oscillator may be the ground state or may not be the ground state.

[0091] FIG4 is a schematic diagram of quantum state changes during a second quantum state preparation according to an embodiment of the present application. Referring to FIG4 , the first spin state is |↑> and the second spin state is |↓>. After the quantum state preparation in step S101, if the state is the ground state |↑,0>, then during the second quantum state preparation, the ground state cannot transition to other energy states, and thus the spin state cannot be changed. The spin state remains the first spin state, and the spin state satisfies the condition. If it is not the ground state, such as |↑,1>, |↑,2>, |↑,3>, |↑,4> in FIG4 , the second quantum state preparation can change the spin state. For example, in FIG4 , the spin state changes from |↑,4> to |↓,3>, from |↑,3> to |↓,2>, from |↑,2> to |↓,1>, and from |↑,1> to |↓,0>. The spin state changes from the first spin state |↑> to the second spin state |↓>, and the spin state does not satisfy the condition.

[0092] For example, a first spin state is used as a target, and quantum state preparation is performed on the oscillator to obtain a oscillator corresponding to the first spin state; a second spin state is used as a target, and quantum state preparation is performed on the oscillator; a spin state detection is performed on the spin state corresponding to the oscillator; when the spin state is the second spin state, the quantum state preparation and spin state detection are repeated until the spin state is the first spin state, thereby obtaining a oscillator in the target quantum state. When the spin state is the first spin state, it indicates that the oscillator in the target quantum state has been obtained, and the quantum state preparation and spin state detection are no longer necessary.

[0093] In the embodiment of the present application, when the oscillator is carried out to quantum state preparation, since it is impossible to ensure that the external state can be prepared to the ground state, but it is possible to ensure that the internal state (spin state) corresponding to the prepared oscillator is obtained, the quantum state preparation operation is performed twice with different spin states as the target. Since the spin state corresponding to the oscillator reaching the ground state does not change, the spin state after the detection quantum state preparation is detected, if the condition is not met, the oscillator is not yet reached to the ground state, and the quantum state preparation is repeated until the spin state after the detection quantum state preparation meets the condition, indicating that the oscillator is in the target quantum state (external state is the ground state). By the cyclic process of quantum state preparation and spin state detection, it is ensured that the oscillator is finally prepared to the target quantum state, and the preparation effect is guaranteed.

[0094] FIG5 is a flow chart of a quantum state preparation method provided in an embodiment of the present application. As shown in FIG5 , the method includes the following steps.

[0095] S201: Trapping N ions to obtain 3N oscillators.

[0096] In the embodiment of the present application, the aforementioned ion trap may be used to trap ions.

[0097] S202: Obtain M resonators from the 3N resonators based on a quantum information processing task.

[0098] Wherein, N is a positive integer, and M is a positive integer less than 3N.

[0099] When the ion trap traps N ions, 3N oscillators will be formed in space, and each oscillator will be in a certain state, which is determined by the temperature when the ions are trapped. Generally speaking, the oscillator state at this time is a thermal state, that is, there is a layout distribution on all the oscillator energy levels. Among the above 3N thermal state oscillators, M oscillators are selected to form a space for processing quantum information. The embodiment of this application does not limit the method of selecting M oscillators, for example, random selection is adopted. According to the requirements of the quantum information processing task, it is necessary to prepare these M oscillators to the ground state through subsequent steps.

[0100] S203: Using the first spin state as a target, performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state.

[0101] In some possible implementations of the present application, the quantum state preparation adopts one of the following methods: sideband cooling technology and rapid adiabatic channel technology. The above technologies can realize quantum state preparation with the goal of setting the spin state.

[0102] In some other possible implementations of the present application, the quantum state preparation may also adopt other cooling technologies.

[0103] Sideband cooling involves applying a suitable laser to excite ions at higher vibrational energy levels to achieve sideband resonant transitions, causing them to transition from a higher vibrational quantum number to a lower one. During this process, the ions release a quantum of vibrational energy, cooling their motion. By repeating this process, the ions' motion can ultimately be effectively cooled to their ground state. The change in quantum state during the preparation process can be expressed as: |↓,n> → |↑,n-1> → |aux,n-1> → |↓,n-1>. The energy levels that achieve these transitions within a single sideband cooling operation depend on the intensity and duration of the laser. However, multiple pulse repetitions can be used to achieve these transitions for all phonon states n on the resonator, reducing the number of phonons and ultimately achieving cooling.

[0104] The rapid adiabatic channel technique achieves consistent population transfer efficiency (the number of atoms / molecules occupying different (energy) levels) for different phonon states with the same laser parameters by applying linear frequency modulation to the driving laser field while smoothly ramping the laser power up and down. The quantum state transition during the preparation process can be expressed as: |↓,n> → |↑,n> → |↓,n-1>. Using the rapid adiabatic channel pulse, this transition is achieved for all n states in a single operation, reducing the phonon population and ultimately achieving cooling.

[0105] FIG6 is a schematic diagram of the sideband Rabi frequency and detuning amount scanning waveform in the fast adiabatic channel technology provided in an embodiment of the present application. Referring to FIG6 , the horizontal axis is t / T, the vertical axis is Δ / Δ0, and Ω / Ω0. The waveform function of the Rabi frequency is Ω=Ω0[sign(T / 2-t)sin(πt / T)], and the waveform function of the detuning amount is Δ=Δ0[sign(T / 2-t)cos(πt / T)]. Wherein, Ω is the intensity of the interaction between the laser and the ion, Ω0 is the unit intensity, T is the duration of the entire pulse, t is a certain moment, Δ is the difference between the frequency of the laser and the ion sideband transition frequency, and Δ0 is the unit difference.

[0106] S204: Using the second spin state as a target, perform quantum state preparation on the oscillator.

[0107] In some possible implementations of the present application, the target quantum state is a ground state, the first spin state is |↑>, and the second spin state is |↓>.

[0108] In some other possible implementations of the present application, the target quantum state is a ground state, the first spin state is |↓>, and the second spin state is |↑>.

[0109] Step S204 can also use sideband cooling technology or rapid adiabatic channel technology to prepare the quantum state. The cooling technology used in step S204 can be the same as that in step S203 or different.

[0110] For example, the quantum state preparation in step S203 adopts the sideband cooling technology, and the quantum state preparation in step S204 adopts the fast adiabatic channel technology.

[0111] For another example, the quantum state preparation in step S203 adopts the sideband cooling technology, and the quantum state preparation in step S204 adopts the sideband cooling technology.

[0112] For another example, the quantum state preparation in step S203 adopts the rapid adiabatic channel technology, and the quantum state preparation in step S204 adopts the rapid adiabatic channel technology.

[0113] For another example, the quantum state preparation in step S203 adopts the rapid adiabatic channel technology, and the quantum state preparation in step S204 adopts the sideband cooling technology.

[0114] S205: Performing spin state detection on the spin state corresponding to the resonator.

[0115] In some possible implementations of the present application, detecting the spin state corresponding to the oscillator includes detecting the spin state corresponding to the oscillator using a state-dependent fluorescence detection technique. Using the state-dependent fluorescence detection technique enables rapid and accurate measurement of the spin state.

[0116] In some other possible implementations of the present application, other detection technologies may also be used to detect the spin state.

[0117] S206: When the spin state satisfies a condition, a resonator of a target quantum state is obtained.

[0118] If the spin state is still the first spin state, the spin state satisfies the condition, and the target quantum state resonator is obtained. If the spin state is the second spin state, the spin state does not satisfy the condition, and step S207 is executed.

[0119] Taking the first spin state as |↑> and the second spin state as |↓> as an example, when step S205 detects that the spin state is |↑>, it means that the spin state meets the conditions, and the oscillator of the target quantum state is obtained.

[0120] When the spin state is detected as |↓> in step S205, it indicates that the spin state does not meet the condition, and step S207 is executed.

[0121] S207: When the spin state does not satisfy the condition, repeat steps S203 to S205 until the spin state satisfies the condition.

[0122] The following uses the rapid adiabatic channel technology as an example to illustrate the process of quantum state preparation and spin state detection:

[0123] Applying a rapid adiabatic process to the ion allows for consistent sideband manipulation of the ion's phonon excited state, causing the ion to collapse to the ground state with a certain probability. Two rapid adiabatic processes are then applied, followed by a measurement of the ion's internal state. If the internal state remains unchanged after the second rapid adiabatic process, the ion has collapsed to the ground state, resulting in a resonator of the target quantum state. Otherwise, two more rapid adiabatic processes and postselective measurements are applied until the ground state is selected, completing the preparation of the corresponding target quantum state.

[0124] In the implementation of the present application, the above steps are performed on M resonators respectively, so that each resonator is finally in the ground state, and the M resonators are prepared to the ground state.

[0125] Long ion chain quantum computing is usually based on high-fidelity initial state preparation. The embodiments of the present application can improve the fidelity of initial state preparation and reduce engineering complexity. The long chain formed by N ions has 3N motion modes, and the frequency of each vibration mode is different. The complex phonon frequency components greatly limit the cooling effect of the multi-ion long chain, which reduces the fidelity of quantum manipulation and further reduces the fidelity of quantum gates, while fast adiabatic channels can be applied to all motion modes. For example, considering a long chain composed of five ions, the quantum state preparation method provided by this application combined with fast adiabatic channels or sideband cooling technology can be used to efficiently cool all motion modes, and the high fidelity of the initial state preparation can be further ensured by post-selection.

[0126] FIG7 is a schematic diagram of the simulation results of quantum state preparation using the method of the present application provided in an embodiment of the present application. Referring to FIG7, according to the simulation results, when the post-selection rate approaches 100%, the fidelity of the initial state preparation can theoretically reach about 99.9%. The figure below shows an estimate of the resource consumption required for post-selection after the initial cooling. The horizontal axis represents the proportion of the ground state after the initial cooling. The left vertical axis of the two vertical axes is the post-selection rate, which represents the percentage of post-selection, indicating the number of post-selections required. The right vertical axis is the error probability that the quantum state obtained after the final post-selection is not in the ground state. Based on the solid curve in FIG7, it can be seen that the higher the proportion of the ground state after the initial cooling, the lower the number of post-selections required, and the lower the proportion of the ground state after the initial cooling, the higher the number of post-selections required. Based on the dotted curve in FIG7, it can be seen that the higher the proportion of the ground state after the initial cooling, the higher the error probability after fewer post-selections, and the lower the proportion of the ground state after the initial cooling, the lower the error probability after multiple post-selections, but the overall numerical range of the error probability is low, resulting in higher fidelity. That is to say, after multiple selections, a high-fidelity ground-state oscillator can be obtained.

[0127] FIG8 is a flow chart of a quantum state preparation method provided in an embodiment of the present application. As shown in FIG8 , the method includes the following steps.

[0128] S301: Trapping N ions to obtain 3N oscillators.

[0129] S302: Obtain M resonators from the 3N resonators based on a quantum information processing task.

[0130] S303: Using the first spin state as a target, performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state.

[0131] S304: Using the second spin state as a target, perform quantum state preparation on the oscillator.

[0132] S305: Perform spin state detection on the spin state corresponding to the resonator.

[0133] Steps S301 to S305 may refer to the aforementioned steps S201 to S205 respectively, and are not described in detail here.

[0134] S306: When the spin state satisfies a condition, a resonator of a target quantum state is obtained.

[0135] If the spin state is still the first spin state, the spin state satisfies the condition, and the target quantum state resonator is obtained. If the spin state is the second spin state, the spin state does not satisfy the condition, and step S307 is executed.

[0136] Taking the first spin state as |↑> and the second spin state as |↓> as an example, when step S305 detects that the spin state is |↑>, it means that the spin state meets the conditions, and the resonator of the target quantum state is obtained.

[0137] When the spin state is detected as |↓> in step S305, it indicates that the spin state does not meet the condition, and step S307 is executed.

[0138] S307: When the spin state does not satisfy the condition, use the first spin state as a target to perform quantum state preparation on the oscillator.

[0139] S308: Perform spin state detection on the spin state corresponding to the resonator.

[0140] If the spin state is still the second spin state, the spin state satisfies the condition, and the target quantum state resonator is obtained. If the spin state is the first spin state, the spin state does not satisfy the condition, and step S309 is executed.

[0141] Taking the first spin state as |↑> and the second spin state as |↓> as an example, when step S308 detects that the spin state is |↓>, it means that the spin state meets the conditions, and the oscillator of the target quantum state is obtained.

[0142] When the spin state is detected as |↑> in step S308, it indicates that the spin state does not meet the condition, and step S309 is executed.

[0143] S309: When the spin state does not satisfy the condition, use the second spin state as a target to perform quantum state preparation on the oscillator.

[0144] S310: Performing spin state detection on the spin state corresponding to the resonator.

[0145] If the spin state is still the first spin state, the spin state satisfies the condition, and the target quantum state resonator is obtained. If the spin state is the second spin state, the spin state does not satisfy the condition, and step S307 is executed.

[0146] Taking the first spin state as |↑> and the second spin state as |↓> as an example, when step S310 detects that the spin state is |↑>, it means that the spin state meets the conditions, and the oscillator of the target quantum state is obtained.

[0147] When step S310 detects that the spin state is |↓>, it means that the spin state does not meet the condition, and step S307 is executed.

[0148] The embodiment of the present application provides a method for preparing a quantum state based on cooling and post-selection. By performing a rapid adiabatic process on the ions, the number of phonons of the oscillator is reduced, and finally the spin state detection is used to determine whether the preparation is successful. If not, the preparation is continued, thereby cycling the rapid adiabatic process and post-selection measurement multiple times to improve the fidelity of the prepared target quantum state. This method can be applied to large-scale long ion chain quantum computing, and can improve the cooling effect of ion chains or other systems with complex motion mode spectra; this method does not require high-fidelity operations for a single cooling, and does not require strict vibration mode spectrum resolution operations, which can greatly simplify the quantum state preparation method.

[0149] Figure 9 is a block diagram of a quantum state preparation device provided in an embodiment of the present application. The quantum state preparation device can be implemented as all or part of a quantum computing system through software, hardware, or a combination of both. The quantum state preparation device may include: a quantum state preparation unit 901, a detection unit 902, and a control unit 903.

[0150] The quantum state preparation unit 901 is used to perform two quantum state preparations on the oscillator in sequence using different spin states as targets.

[0151] A detection unit 902 is configured to perform spin state detection on the spin state corresponding to the resonator;

[0152] The control unit 903 is used to control the quantum state preparation unit and the detection unit to repeat the quantum state preparation and the spin state detection when the spin state does not meet the conditions, until the spin state meets the conditions, thereby obtaining a resonator of the target quantum state.

[0153] Optionally, the spin state satisfies a condition including:

[0154] The spin state has not changed after the last quantum state preparation.

[0155] Optionally, the target quantum state is prepared by taking a first spin state as a target and performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state; and taking a second spin state as a target and performing quantum state preparation on the oscillator;

[0156] The control unit 903 is configured to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

[0157] Optionally, the target quantum state is prepared by taking a first spin state as a target and performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state; and taking a second spin state as a target and performing quantum state preparation on the oscillator;

[0158] The control unit 903 is configured to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

[0159] Optionally, the device further includes: an ion trapping unit 904 and an acquisition unit 905 .

[0160] The ion trapping unit 904 is used to trap N ions to obtain 3N resonators, where N is a positive integer.

[0161] The acquisition unit 905 is configured to acquire M resonators from the 3N resonators based on a quantum information processing task, where M is a positive integer less than 3N.

[0162] Optionally, the M oscillators prepare quantum states respectively through M cycles.

[0163] It should be noted that the quantum state preparation device provided in the above embodiment is only illustrated by the division of the above functional units when performing quantum state preparation. In actual applications, the above functions can be assigned to different functional units as needed, that is, the internal structure of the device can be divided into different functional units to complete all or part of the functions described above. In addition, the quantum state preparation device provided in the above embodiment and the quantum state preparation method embodiment are based on the same concept. The specific implementation process is detailed in the method embodiment and will not be repeated here.

[0164] An embodiment of the present application also provides a quantum computing system, which includes a quantum state preparation device as shown in FIG9 .

[0165] Figure 10 shows a schematic diagram of the structure of an electronic device 150 provided in an embodiment of the present application. The electronic device 150 shown in Figure 10 is used to perform the operations involved in the quantum state preparation method shown in any of Figures 3 to 8 above. The electronic device 150 can be part of the aforementioned quantum state preparation system, used to control the quantum state preparation device to implement the quantum state preparation method. The electronic device 150 can be implemented using a general bus architecture.

[0166] As shown in FIG. 10 , the electronic device 150 includes at least one processor 151 , a memory 153 , and at least one communication interface 154 .

[0167] The processor 151 is, for example, a general-purpose central processing unit (CPU), a digital signal processor (DSP), a network processor (NP), a data processing unit (DPU), a microprocessor, or one or more integrated circuits for implementing the solution of the present application. For example, the processor 151 includes an application-specific integrated circuit (ASIC), a programmable logic device (PLD) or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The PLD is, for example, a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof. It can implement or execute the various logic blocks, modules, and circuits described in conjunction with the disclosure of the embodiments of the present application. The processor can also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, and the like.

[0168] Optionally, the electronic device 150 further includes a bus. The bus is used to transmit information between the components of the electronic device 150. The bus may be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, for example. Buses can be classified as address buses, data buses, control buses, and the like. For ease of illustration, FIG10 shows only one thick line, but this does not imply that there is only one bus or only one type of bus.

[0169] The memory 153 is, for example, a read-only memory (ROM) or other type of static storage device that can store static information and instructions, a random access memory (RAM) or other type of dynamic storage device that can store information and instructions, an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, an optical disc storage (including a compact disc, laser disc, optical disc, digital versatile disc, Blu-ray disc, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited thereto. The memory 153 is, for example, independent and connected to the processor 151 via a bus. The memory 153 can also be integrated with the processor 151.

[0170] The communication interface 154 uses any transceiver-like device to communicate with other devices or communication networks. The communication network can be Ethernet, a radio access network (RAN), or a wireless local area network (WLAN). The communication interface 154 can include a wired communication interface and a wireless communication interface. Specifically, the communication interface 154 can be an Ethernet interface, a Fast Ethernet (FE) interface, a Gigabit Ethernet (GE) interface, an Asynchronous Transfer Mode (ATM) interface, a wireless local area network (WLAN) interface, a cellular network communication interface, or a combination thereof. The Ethernet interface can be an optical interface, an electrical interface, or a combination thereof. In an embodiment of the present application, the communication interface 154 can be used for the electronic device 150 to communicate with other devices.

[0171] In a specific implementation, as an example, the processor 151 may include one or more CPUs, such as CPU0 and CPU1 shown in FIG10 . Each of these processors may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. The processor herein may refer to one or more devices, circuits, and / or processing cores for processing data (e.g., computer program instructions).

[0172] In a specific implementation, as an embodiment, the electronic device 150 may include multiple processors, such as the processor 151 and the processor 155 shown in FIG10 . Each of these processors may be a single-core processor (single-CPU) or a multi-core processor (multi-CPU). The processor herein may refer to one or more devices, circuits, and / or processing cores for processing data (such as computer program instructions).

[0173] In a specific implementation, as an embodiment, the electronic device 150 may further include an output device and an input device. The output device communicates with the processor 151 and can display information in a variety of ways. For example, the output device can be a liquid crystal display (LCD), a light emitting diode (LED) display device, a cathode ray tube (CRT) display device, or a projector. The input device communicates with the processor 151 and can receive user input in a variety of ways. For example, the input device can be a mouse, a keyboard, a touch screen device, or a sensor device.

[0174] In some embodiments, the memory 153 is used to store program code 1510 for executing the solution of the present application, and the processor 151 can execute the program code 1510 stored in the memory 153. That is, the electronic device 150 can implement the quantum state preparation method provided by the method embodiment by executing the program code 1510 in the memory 153 through the processor 151. The program code 1510 may include one or more software modules. Optionally, the processor 151 itself may also store program code or instructions for executing the solution of the present application.

[0175] In a specific embodiment, the electronic device 150 of the embodiment of the present application may correspond to the controller in the above-mentioned method embodiments, and the processor 151 in the electronic device 150 reads the instructions in the memory 153, so that the electronic device 150 shown in Figure 10 can execute all or part of the operations performed by the controller.

[0176] Specifically, the processor 151 is used to control the quantum state preparation device to use different spin states as targets, and perform quantum state preparation on the oscillator twice in sequence; perform spin state detection on the spin state corresponding to the oscillator; when the spin state does not meet the conditions, repeat the quantum state preparation and the spin state detection until the spin state meets the conditions, thereby obtaining the oscillator of the target quantum state.

[0177] For the sake of brevity, other optional implementations will not be described here in detail.

[0178] Among them, each step of the quantum state preparation method shown in any one of Figures 3 to 8 is completed by the hardware integrated logic circuit or software instructions in the processor of the electronic device 150. The steps of the method disclosed in conjunction with the embodiment of the present application can be directly embodied as being executed by a hardware processor, or can be executed by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the art such as random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory, registers, etc. The storage medium is located in the memory, and the processor reads the information in the memory and completes the steps of the above method in combination with its hardware. To avoid repetition, it will not be described in detail here.

[0179] An embodiment of the present application further provides a chip comprising an input interface, an output interface, a processor, and a memory. The input interface, the output interface, the processor, and the memory are connected via an internal connection path. The processor is configured to execute code stored in the memory. When the code is executed, the processor is configured to perform any of the aforementioned quantum state preparation methods.

[0180] It should be understood that the processor may be a CPU, or other general-purpose processor, DSP, ASIC, FPGA or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. It is worth noting that the processor may be a processor supporting the ARM architecture.

[0181] Furthermore, in an optional embodiment, there are one or more processors and one or more memories. Alternatively, the memories may be integrated with the processors, or provided separately from the processors. The memories may include read-only memory and random access memory, and provide instructions and data to the processors. The memories may also include non-volatile random access memory. For example, the memories may also store reference blocks and target blocks.

[0182] The memory may be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. The non-volatile memory may be ROM, PROM, EPROM, EEPROM, or flash memory. The volatile memory may be RAM, which serves as an external cache. By way of example and not limitation, many forms of RAM are available, including, for example, SRAM, DRAM, SDRAM, DDR SDRAM, ESDRAM, SLDRAM, and DR RAM.

[0183] In an embodiment of the present application, a computer-readable storage medium is also provided, which stores computer instructions. When the computer instructions stored in the computer-readable storage medium are executed by an electronic device, the electronic device executes the quantum state preparation method provided above.

[0184] In an embodiment of the present application, a computer program product containing instructions is also provided. When the computer program product is run on an electronic device, the electronic device executes the quantum state preparation method provided above.

[0185] In the above embodiments, all or part of the embodiments may be implemented by software, hardware, firmware, or any combination thereof. When implemented using software, all or part of the embodiments may be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described herein are generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated therein. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a magnetic tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state drive).

[0186] Those skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware, or by a program to instruct the relevant hardware, and the program may be stored in a computer-readable storage medium, which may be a read-only memory, a disk, or an optical disk, etc.

[0187] The above are merely optional embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

[0188] Unless otherwise defined, the technical or scientific terms used herein shall have the usual meaning understood by persons of ordinary skill in the field to which this application belongs. The words “first”, “second”, “third” and similar terms used in the patent application specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as “a” or “an” do not indicate a quantitative limitation, but rather indicate the presence of at least one. Words such as “include” or “comprising” and similar words mean that the elements or objects appearing before “include” or “comprising” cover the elements or objects listed after “include” or “comprising” and their equivalents, and do not exclude other elements or objects.

[0189] The above is only an embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a quantum state, characterized in that: The method comprises: Using different spin states as targets, the quantum state preparation of the oscillator was performed twice in sequence; Performing spin state detection on the spin state corresponding to the resonator; In the case that the spin state does not satisfy the condition, the quantum state preparation and the spin state detection are repeated until the spin state satisfies the condition, thereby obtaining a resonator of a target quantum state.

2. The method for preparing a quantum state according to claim 1, wherein: The spin state satisfies the following conditions: The spin state has not changed after the last quantum state preparation.

3. The method for preparing a quantum state according to claim 1 or 2, wherein: The method uses different spin states as targets and sequentially performs two quantum state preparations on the oscillator, including: Using the first spin state as a target, the oscillator is subjected to quantum state preparation to obtain a oscillator corresponding to the first spin state; using the second spin state as a target, the oscillator is subjected to quantum state preparation; The repeating of the quantum state preparation comprises: In each cycle, the first spin state and the second spin state are sequentially used as targets to perform two quantum state preparations on the oscillator.

4. The method for preparing a quantum state according to claim 1 or 2, wherein: The method uses different spin states as targets and sequentially performs two quantum state preparations on the oscillator, including: Using the first spin state as a target, the oscillator is subjected to quantum state preparation to obtain a oscillator corresponding to the first spin state; using the second spin state as a target, the oscillator is subjected to quantum state preparation; The repeating of the quantum state preparation comprises: In odd cycles, the first spin state is used as a target to prepare the quantum state of the oscillator; in even cycles, the second spin state is used as a target to prepare the quantum state of the oscillator.

5. The method for preparing a quantum state according to any one of claims 1 to 4, characterized in that: The method further comprises: Trapping N ions, we get 3N oscillators, where N is a positive integer; Based on the quantum information processing task, M resonators are obtained from the 3N resonators, where M is a positive integer less than 3N.

6. The method for preparing a quantum state according to claim 5, wherein: The M oscillators are respectively subjected to quantum state preparation through M cycles.

7. A quantum state preparation device, characterized in that: The device comprises: A quantum state preparation unit is used to sequentially perform two quantum state preparations on the oscillator using different spin states as targets; A detection unit, configured to perform spin state detection on the spin state corresponding to the resonator; A control unit is used to control the quantum state preparation unit and the detection unit to repeat the quantum state preparation and the spin state detection when the spin state does not meet the conditions, until the spin state meets the conditions, thereby obtaining a resonator of the target quantum state.

8. The quantum state preparation device according to claim 7, characterized in that: The spin state satisfies the following conditions: The spin state has not changed after the last quantum state preparation.

9. The quantum state preparation device according to claim 7 or 8, characterized in that: The target quantum state is obtained by using the first spin state as the target and performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state; and by using the second spin state as the target and performing quantum state preparation on the oscillator; The control unit is used to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

10. The quantum state preparation device according to claim 7 or 8, characterized in that: The target quantum state is obtained by using the first spin state as the target and performing quantum state preparation on the oscillator to obtain a oscillator corresponding to the first spin state; and by using the second spin state as the target and performing quantum state preparation on the oscillator; The control unit is used to control the quantum state preparation unit to sequentially use the first spin state and the second spin state as targets in each cycle to perform two quantum state preparations on the oscillator.

11. The quantum state preparation device according to any one of claims 7 to 10, characterized in that: The device further comprises: The ion trapping unit is used to trap N ions to obtain 3N resonators, where N is a positive integer; An acquisition unit is used to acquire M resonators from the 3N resonators based on a quantum information processing task, where M is a positive integer less than 3N.

12. The quantum state preparation device according to claim 11, characterized in that: The M oscillators are respectively subjected to quantum state preparation through M cycles.

13. A quantum computing system, characterized in that The quantum computing system comprises the quantum state preparation device according to any one of claims 7 to 12.

14. A quantum state preparation device, characterized in that: The quantum state preparation device includes a processor and a memory, the memory is used to store a software program, and the processor runs or executes the software program stored in the memory so that the quantum state preparation device implements the method according to any one of claims 1 to 6.

15. A computer-readable storage medium, characterized in that The computer-readable storage medium is used to store program codes executed by a processor, wherein the program codes include instructions for implementing the method according to any one of claims 1 to 6.

16. A computer program product, characterized in that The computer program product comprises program codes, and when a computer runs the computer program product, the computer is caused to perform the method according to any one of claims 1 to 6.

Images