Efficient cooling of ion chains for quantum computing

Abstract

The present disclosure describes various aspects of a technique for cooling an ion chain to a near combined ground state that does not scale with the number of ions in the chain. By individually addressing each ion and using each ion to cool a different mode of motion, the modes of motion can be cooled simultaneously. In one example, one-third of all modes of motion can be cooled simultaneously. In one aspect, the technique includes: generating a sideband cooling laser beam for each ion in the ion chain; using corresponding sideband cooling laser beams to simultaneously cool two or more modes of motion associated with the ions in the ion chain until each of the two or more modes of motion reaches a ground state of motion; and after the two or more modes of motion reach the ground state of motion, using the ion chain to perform quantum computations.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 692,099, filed on June 29, 2018, entitled “EFFICIENT COOLING OF ION CHAINS FOR QUANTUM COMPUTATION,” and U.S. Patent Application No. 16 / 450,779, filed on June 24, 2019, entitled “EFFICIENT COOLING OF ION CHAINS FOR QUANTUM COMPUTATION,” the entireties of which are expressly incorporated herein by reference. Technical Field

[0003] Various aspects of the present disclosure relate generally to quantum systems and, more particularly, to efficient cooling of ion chains of atomic quantum bits (qubits) used in quantum computing. Background Art

[0004] Trapped atoms are one of the leading implementations of quantum information processing. Atom-based qubits can be used as quantum gates in quantum memories, quantum computers and simulators, and can act as nodes in quantum communication networks.

[0005] Entanglement gates need to be performed between physical qubits in the ion chain to achieve large-scale quantum computing. To this end, quantum computing with trapped atomic ions (qubits) uses the combined motion of the ions to create entangled gates. Since the initial motion state affects the gate operation, the ions are usually first cooled to a near motion ground state at the beginning of the quantum computation or during the quantum computation (if sympathetic cooling is used). The number of motion modes that need to be cooled is proportional to the number of ions. Traditionally, motion modes are cooled sequentially, that is, the next motion mode is cooled only after the previous motion mode is cooled. As the number of atomic ions increases, this results in a longer total cooling time.

[0006] As the cooling process is prolonged, the heating of the motion modes by the electric field fluctuations in the ion trap electrodes can generate noise that overwhelms the cooling process. Therefore, it is advantageous to implement faster cooling methods. Therefore, a technique that allows for more efficient cooling of ion chains is needed. Summary of the invention

[0007] The following is a brief summary of one or more aspects in order to provide a basic understanding of these aspects. This summary is not an extensive overview of all contemplated aspects, and is neither intended to identify the core or key elements of all aspects, nor to delineate the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be presented later.

[0008] The present disclosure describes techniques for cooling an ion chain to near a composite motion ground state that does not grow as the number of ions increases in execution time. Multiple motion modes can be cooled simultaneously by addressing each ion individually and using each ion to cool a different motion mode. In one example, one-third of all motion modes can be cooled simultaneously. In other examples, other numbers of all motion modes can be cooled.

[0009] In one aspect of the present disclosure, a method for cooling an ion chain having a plurality of ions is described, the method comprising: generating a sideband cooling laser beam for each ion in the ion chain; using a corresponding sideband cooling laser beam to simultaneously cool two or more motion modes associated with the ions in the ion chain until each of the two or more motion modes reaches a motion ground state; and performing quantum computing using the ion chain after the two or more motion modes reach the motion ground state.

[0010] In another aspect of the present disclosure, a quantum information processing (QIP) system for cooling an ion chain having a plurality of ions is described, the system comprising: one or more light sources configured to generate a sideband cooling laser beam for each ion in the ion chain; a beam controller configured to use corresponding sideband cooling laser beams to simultaneously cool two or more motion modes associated with the ions in the ion chain until each of the two or more motion modes reaches a motion ground state; and an algorithm component configured to perform quantum computing using the ion chain after the two or more motion modes reach the motion ground state.

[0011] In another aspect of the present disclosure, a computer-readable storage medium storing code is described, the code having instructions executable by a processor for cooling an ion chain having a plurality of ions, the instructions comprising: code for generating a sideband cooling laser beam for each ion in the ion chain; code for simultaneously cooling two or more motion modes associated with the ions in the ion chain using corresponding sideband cooling laser beams until each of the two or more motion modes reaches a motion ground state; and code for performing quantum computing using the ion chain after the two or more motion modes reach the motion ground state. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings depict only some embodiments and therefore should not be considered limiting in scope.

[0013] Figure 1A A diagram showing a trap holding atomic ions forming a linear crystal or lattice is illustrated in accordance with aspects of the present disclosure.

[0014] Figure 1B is a diagram illustrating an example of a simplified energy level diagram showing application of laser radiation for state initialization in accordance with aspects of the present disclosure.

[0015] Figure 1C is a diagram illustrating an example of a simplified energy level diagram showing application of laser radiation for qubit state detection by fluorescence in accordance with aspects of the present disclosure.

[0016] Figure 2 is a diagram showing an example of a sequential sideband cooling process.

[0017] Figure 3 is a diagram illustrating an example of a chain with four (4) ions confined in an electric potential in accordance with aspects of the present disclosure.

[0018] Figure 4 is a diagram illustrating an example of a distribution of a set of N=4 motion patterns in accordance with aspects of the present disclosure.

[0019] Figure 5A and Figure 5B It is a method for describing various aspects of the present disclosure. Figure 4 Illustration of an example of the amplitude of ion motion in a set of patterns.

[0020] Figure 6 is a diagram illustrating an example of parallelization or synchronization of sideband cooling processes according to aspects of the present disclosure.

[0021] Figure 7 is a diagram illustrating an example of a computer device according to aspects of the present disclosure.

[0022] Figure 8 is a flow chart illustrating an example of a method according to aspects of the present disclosure.

[0023] Fig. 9A is a block diagram illustrating an example of a quantum information processing (QIP) system according to aspects of the present disclosure.

[0024] Fig. 9B is a block diagram illustrating an example of an optical controller used in conjunction with parallelized sideband cooling in accordance with aspects of the present disclosure. DETAILED DESCRIPTION

[0025] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known components are shown in block diagram form to avoid blurring these concepts.

[0026] As described above, trapped atoms can be used to implement quantum information processing. Atom-based qubits can be used as different types of devices, including but not limited to quantum memories, quantum gates in quantum computers and simulators, and nodes of quantum communication networks. Qubits based on trapped atomic ions can have very good coherence, can be prepared and measured with close to 100% efficiency, and can be easily entangled with each other by modulating their Coulomb interactions with suitable external control fields (such as light fields or microwave fields). As used in this disclosure, the terms "atomic ions", "atoms" and "ions" can be used interchangeably to describe particles that will be confined or actually confined in a trap to form a chain, crystal, lattice or similar arrangement or configuration. The present disclosure describes a method or process for cooling the motion patterns in a crystal of trapped atomic ions and a technology in the form of an apparatus or device.

[0027] A typical ion trap geometry or structure for quantum information and metrology purposes is a linear radio frequency (RF) Paul trap (also called an RF trap, or simply a Paul trap), in which nearby electrodes maintain static and dynamic potentials, which results in effective inhomogeneous harmonic confinement of ions. An RF Paul trap is a trap that uses an electric field to capture or confine charged particles to a specific area, position, or location. When atomic ions are laser-cooled to very low temperatures in such a trap, the atomic ions form a stable crystal of qubits (e.g., a structured arrangement of qubits), with Coulomb repulsion balancing the external confinement forces. For sufficient trap anisotropy, ions can form linear crystals along weak confinement directions, and this is the arrangement typically used for applications in quantum information and metrology.

[0028] The present disclosure describes techniques for cooling an ion chain (e.g., an ion lattice or an ion crystal) to near a composite motion ground state that does not grow as the number of ions increases in execution time. By addressing each ion individually and using each ion to cool a different motion mode, the motion modes can be cooled simultaneously. In one example, one-third of all motion modes can be cooled simultaneously.

[0029] Figure 1A The illustration shows a diagram of trapping atomic ions in a linear crystal 110 using a linear RF Paul trap (using electrodes inside the vacuum chamber), for example, in a vacuum chamber 100. Figure 1A In the example shown in , the vacuum chamber in the quantum system may include a vacuum chamber for trapping N (N ≥ 1) atomic ytterbium ions (e.g., 171 Yb + ions) that are confined in a linear crystal 110 and can be laser cooled to near rest. The number of trapped atomic ions is configurable. 171 Yb + The resonant laser radiation illuminates the atoms and images the fluorescence of the atomic ions onto a camera. In one example, the atomic ions can be separated from each other by a distance of about 5 micrometers (μm) 115, which can be verified by fluorescence. The separation of the atomic ions is determined by the balance between external restraining forces and Coulomb repulsion.

[0030] The strong fluorescence of each trapped atomic ion relies on the efficient recycling of photons, and the atomic ion species are selected for strongly closed optical transitions, which allows laser cooling of the motion, qubit state initialization, and efficient qubit readout. Inside these atomic ions, the qubit can be represented by two stable electronic energy levels, usually characterized by an effective spin with two states |↑> and |↓>, or equivalently |1> and |0>. For example, Figure 1B and Figure 1C Atomic ions are shown separately 171 Yb + Simplified energy level diagrams 120 and 150 of FIG. 1 , where the qubit energy levels |↑> and |↓> 130 are represented by stable hyperfine levels in the electronic ground state and are separated by a frequency ω0 / 2π = 12.642812 GHz. 171 Yb + The electronic excited states |e> and |e′>140 in are themselves split by a small hyperfine coupling and separated from the ground state by an optical separation with an energy corresponding to a wavelength of light of 369.53 nm.

[0031] Laser radiation tuned to just below resonance in these optical transitions allows Doppler laser cooling to confine atomic ions near the bottom of the trap. Other more complex forms of laser cooling can bring atomic ions to near rest in the trap, as will be discussed in this disclosure.

[0032] When with and When a two-color laser beam (e.g., a beam with two tones resulting from optical modulation of the sidebands) is applied to the atom, it rapidly enters the state |↓> and no longer interacts with the light field, allowing the qubit to be initialized with essentially 100% fidelity (e.g., see Figure 1B ).

[0033] When applied with When a single laser beam is applied to the transition resonance, the closed-loop optical transition causes the ions in the |↑> state to fluoresce strongly, while the ions in the |↓> state remain dark due to the laser frequency being far from their resonance (see, for example, Figure 1C ). Collecting even a small fraction of this fluorescence allows detection of the atomic qubit state with near-perfect efficiency or precision. Other atomic species may have similar initialization / detection schemes.

[0034] exist Figure 1B and Figure 1C In FIG. 1 , all allowed transitions from excited electronic states |e> and |e′> 140 are shown as downward wavy arrows. On the other hand, the applied laser radiation (which is shown as upward straight arrows) drives these transitions for initialization to the state |↓>, as Figure 1B , and is used for fluorescence detection of qubit states (|↑>=fluorescence, |↓>=no fluorescence), as shown in Figure 1C as shown in .

[0035] In addition to Doppler laser cooling, sideband cooling processes of ions are also used, in which a laser beam or a combination of laser beams is used to remove a single quantum or multiple quanta of motion from the quantized collective motion of a collection of trapped ions. Figure 2 A diagram 200 is shown describing a current sequential technique for sideband cooling. Figure 2 As shown in diagram 200 in FIG, sideband cooling proceeds in the following steps: (1) the ions are reset to a lower energy state using a "re-pumping" laser beam (see, e.g., 210); (2) the motion-dependent laser interaction transfers the motion of one quantum into a state change from a lower internal energy state to a higher internal energy state (see, e.g., 220); (3) the ions are reset again; and (4) repeating from (2) until most or all of the energy quanta are removed.

[0036] The timing of step (2) is varied during the repetition process shown in step (4) to maximize the quantum removal rate. The timing can also be changed for the specific motion state being cooled. Tens to hundreds of repetitions (or more) may be required to remove enough motion quanta to allow high-quality quantum operations on atoms / ions. For ion chains, the process can usually be repeated for each of the collective modes of motion.

[0037] exist Figure 2 In the example of FIG. 2 , two motion modes (eg, motion mode 1 ( 210 a ) and motion mode 2 ( 210 b )) are shown in conjunction with the “re-pumping” laser beam operation 210 , but additional motion modes may also be cooled after the first two motion modes are cooled. Figure 2 Also shown is a motion transfer operation 220, in which, as described in step (2) above, the motion-dependent laser interaction transfers the motion of a quantum into a state change from a lower internal energy state to a higher internal energy state. Each subsequent transfer is shown to take longer until the particular motion mode finally reaches its motion ground state and the next motion mode can be sideband cooled.

[0038] Unlike the sequential (e.g., continuous or serial) sideband cooling described above, the present disclosure describes performing mode cooling on multiple modes simultaneously or synchronously (e.g., in parallel), which can significantly reduce the time required to cool all modes. For illustrative purposes, an example with four ions is used to describe this simultaneous process. However, the technique can be applied to any number of ions that are trapped in a common trap, even in separate traps, or a combination of both.

[0039] Figure 3 Diagram 300 shows four ions fully confined in an electric potential (e.g., within a Paul trap). For N ions, there are 3×N combined motion modes, typically forming 3 separate groups of N modes each. In this example, one group of N modes is used; however, the method can address any N modes coupled to a sideband cooling laser beam (e.g., addressing beams 310a, 310b, 310c, and 310d). For chains of two or more ions, then N≥2.

[0040] Figure 4 A diagram 400 shows an example of a distribution of a set of N motion mode frequencies for N=4 modes. The motion modes may include one or more longitudinal or axial modes about the ion chain, one or more transverse or radial modes about the ion chain, or a combination thereof.

[0041] Figure 5A and Figure 5BGraphs 500, 510, 520, and 530 depicting an exemplary set of ion motion amplitudes for each of the N=4 modes are shown. In graph 500, the amplitudes associated with frequency f1 Figure 4 The motion mode 1 (mode 1) in is addressed by the second ion (shaded ion 2) in the four-ion chain. In the diagram 510, the frequency associated with f2 Figure 4 The motion mode 2 (mode 2) in is addressed by the third ion (shaded ion 3) in the four-ion chain. In the diagram 520, the frequency associated with f3 Figure 4 The motion mode 3 (mode 3) in is addressed by the fourth ion (shaded ion 4) in the four-ion chain. In diagram 530, the frequency associated with f4 Figure 4 The motion mode 4 (mode 4) in is addressed by the first ion in the four-ion chain (shaded ion 1).

[0042] like Figure 3 As shown in FIG. 1 , each ion is addressed by a sideband cooling laser (or a combination of lasers). Each addressing beam (e.g., addressing beams 1 (310a), 2 (310b), 3 (310c), and 4 (310d)) is tuned to be different from Figure 4 For optimal cooling, the ions addressed by each beam should have large amplitudes in the mode of motion to which the beam is tuned, cf. Figure 5A and Figure 5B .

[0043] Since each beam is localized to a specific ion and a specific mode in the chain, the process of transferring the motion quanta to the internal states of the ions in step (2) above is largely independent for each beam and can occur simultaneously. The reset of steps (1) and (3) is identical and common to all ions. Figure 2 Sequential addressing in the motion state is now Figure 6 600. This parallelization results in a reduction of N times in the time required to cool the ion chain.

[0044] In addition to the general technique of simultaneous or synchronous sideband cooling described above, other aspects can be achieved based on the ability to individually address ions using separate laser beams. For example, in a first aspect, the ions in the chain can be of two or more species or isotopes (e.g., one type of ion is 171 Yb + , and another type of ion is different from 171 Yb +, and used for cooperative cooling). This allows cooperative cooling to be performed during quantum operations (rather than waiting for sideband cooling to complete before performing quantum operations). On the other hand, the single motion mode can be addressed by two or more ions and two or more laser beams. In this case, cooling pulses can be applied sequentially to transfer more than one quantum to multiple ions before applying repumping. On the other hand, the repumping beams can be addressed individually so that sideband cooling of each ion can be performed asynchronously without aligning repumping pulses on all ions.

[0045] Additional details and background of the technique for simultaneous or synchronous sideband cooling of multiple motion modes by individually addressing ions in a chain are described below.

[0046] Cooling the ions in a chain (e.g. an ionic crystal or ionic lattice) to a ground state of motion (motional ground state) is one of the starting steps for any quantum operation or computation. This is usually done via various laser interactions. One of the challenges is that as the number of ions (e.g. the number of qubits) increases, the number of degrees of freedom of the ions that need to be considered for cooling increases. Therefore, as the number of ions increases, the time required to cool the ions also increases, which can lead to the unfavorable situation where the time to cool the ions is longer than the time to perform the quantum operation or computation. Furthermore, ion traps (e.g. Paul traps) can end up heating the ions, which is the opposite of the cooling performed on the ions.

[0047] Since the quantum information processing (QIP) system described in this article is able to address each ion in the chain individually, these capabilities can be used to cool all the motion modes in a group in parallel (or at least one-third of all possible motion modes). In this way, each ion can be simultaneously addressed to a different motion mode, because they are largely independent. Therefore, the repetitive process of removing quantum can be performed on all N modes simultaneously until all motion modes reach the motion ground state.

[0048] Modes of motion may refer to normal modes of motion. For example, the ions in a chain may behave like weights on a spring chain (e.g., coupled oscillators), and their motion may be represented by a set of oscillation frequencies. Thus, modes of motion may correspond to different oscillation frequencies. Normal modes of motion may represent decoupled degrees of freedom, and one may be excited without exciting the others. Due to this decoupling, one normal mode may be hot (e.g., excited) while another normal mode may be cold (e.g., unexcited). Therefore, in order to prepare an ion chain for quantum manipulation or computation, it may be necessary to cool the separated or decoupled normal modes of motion (e.g., modes of motion).

[0049] Previous techniques for sideband cooling of ions have relied on sequential cooling as described above. That is, the first mode in the motion spectrum is cooled, then the second mode, then the third mode, until all modes are cooled. These techniques have several problems. The first is that the process takes a long time to complete, and the second is that before the process is complete, the earlier modes begin to heat up. As a result, this sequential approach is not scalable, especially as the number of ions required for quantum computing and manipulation increases.

[0050] The problems associated with the sequential cooling described above can be overcome by individually addressing the ions supported by the QIP system described herein. Individual addressing of ions also allows for a variety of optimization techniques. For example, in the case of N=3 (three motion modes or normal modes of motion), the motion of each ion can be controlled using a separate laser beam for each ion. So this is a case of 3 ions and 3 normal modes. One of the modes may be that the center or middle ion does not move at all or participate in the motion. In this case, it is inefficient to irradiate the laser beam on the center or middle ion because the middle ion is not coupled. Based on this example, it is clear that some ions are more effectively coupled to certain motion modes (e.g., the end ions in this example) and some ions are idle (e.g., the center or middle ions). Therefore, it is possible to identify which ion (or ions) is best suited for cooling a particular motion mode, and then irradiate or provide a laser beam to that particular ion at a frequency associated with the corresponding motion mode to cool that motion mode through the ion. As described above, Figure 4 The diagram 400 in FIG. 4 shows an example of the correspondence between different frequencies and different modes when N=4, and Figure 5A and Figure 5B Diagrams 500, 510, 520 and 530 in FIG. 5 show examples of how different ions may be used for different modes / frequencies.

[0051] As described above, cooling is gradual and requires removing one quantum of energy from each mode of motion at each step in a series of repeated steps (e.g., see steps (1), (2), (3), and (4) above). Typically, the information qubit in the chain is set or reset to ground and then transferred using a laser beam (e.g., a gate laser). All ions are simultaneously hit by their corresponding gate lasers, where each of these lasers is tuned to a specific frequency to address a specific mode (e.g., see Figure 3 and Figure 4). Each laser pulls one quantum into the internal information state and then is erased, causing the information to be lost or destroyed, but resulting in one quantum being removed from motion. This process of having a gate beam or gate laser interact with the ions to pull motion information into the internal state and then erase is repeated multiple times. In some examples, more than one laser may be tuned to the same frequency to address the same pattern so that multiple quanta of motion are removed from the pattern at once.

[0052] Another optimization that can be made during simultaneous or synchronous sideband cooling is that the amount of time a gate laser or beam interacts with its corresponding ion can be different than the amount of time another gate laser or beam interacts with its corresponding ion. That is, different amounts of time may be required to interact with different ions to address different motion patterns.

[0053] Another optimization that can be performed includes erasing (eg, removing quanta of motion) at different times for different motion modes or ions.

[0054] Other aspects that may need optimization include when the frequencies of certain modes of motion are very close together, and addressing the modes of motion individually may be challenging if the corresponding beams for these modes are close to each other. One approach could be to select an ion for each closely spaced mode using the criterion that the ion has strong coupling only to that mode and no strong coupling to other modes. Figure 5A and Figure 5B The amplitude of the motion in the diagram shows the variation in coupling strength.

[0055] Also as mentioned above, there are usually two different cooling stages. The first is Doppler cooling, and the second is sideband cooling. Doppler cooling can usually bring the number of motion quanta to a few quanta, but not all the way to the ground state of motion. Therefore, Doppler cooling ultimately reduces the motion mode to a few quanta, which is reasonable for the first cooling stage. For sideband cooling, the remaining motion quanta are removed to bring the motion mode to the ground state of motion. Generally, the number of steps or repetitions can be determined so that the removal process is repeated a predetermined number of times, and the predetermined number of repetitions ensures that there are no remaining motion quanta in any motion mode.

[0056] like Figure 2 and Figure 6 As shown in , as the number of quanta gets lower, it takes longer to remove the next quantum from the motion pattern (e.g., the pulse width gets wider as time goes on). This is partly because of the time required to absorb the intra-qubit transition of one of the quanta and then reset (e.g., the process of taking entropy from the system / pattern). Because the amount of time required to remove each additional quantum of motion increases, the amount of time dedicated to each step or repetition must be controlled, as shown in Figure 2 and Figure 6The motion of the transferred laser beam is shown by the variation of the pulse width.

[0057] Another aspect to consider and described above is that due to the uncontrolled electric field fluctuations in the trap electrodes, and because ions are charged particles, the ions will be heated by the electrodes in the ion trap. This effect is called the heating rate. Therefore, one benefit of simultaneous or synchronous sideband cooling is that it is efficient and fast enough so that there is enough time to perform quantum calculations or operations before the motion mode starts to heat up again (e.g., due to the heating rate). In general, it is desirable that the cooling rate is faster than the heating rate.

[0058] One thing to point out is that not all motion modes heat up at the same rate. For example, common modes (e.g., having motion in the same direction) may be more easily excited with a slowly fluctuating electric field (or an electric field that tends to be uniform over the length range of the spatial frequency of the mode), while differential modes (e.g., having motion in different directions) may require rapidly fluctuating electric fields (or electric fields with high spatial frequencies compared to the spatial frequency of the mode) to be excited. Therefore, another optimization opportunity associated with simultaneous sideband cooling is that more time and more resources (e.g., laser beams) can be spent cooling motion modes that heat up faster, while less time and fewer resources can be spent cooling motion modes that heat up slower. For example, more ions and laser beams can be allocated to cool those motion modes that heat up faster. In one example, if there is a remaining motion mode that needs to be cooled, two or more ions and laser beams can be allocated to remove any remaining motion quanta from the motion mode more quickly.

[0059] The QIP systems described herein (see, e.g., Fig. 9A and Fig. 9B Another benefit of ) and its use in simultaneous sideband cooling is the ability to perform cooperative cooling while performing quantum computations or operations as described above. By using two different types of ions or isotopes, where at least one type (atomic species or isotope) is used for computation and at least one type (atomic species or isotope) is interspersed among the computational ions for cooling (cooling or coolant ions), coolant ions can be used to cool nearby computational ions while the computational ions are being used to perform quantum computations or operations. One optimization opportunity is to place or position the coolant ions (co-ions) where they will participate in motion modes to help cool those motion modes.

[0060] The above aspects and combinations of efficient cooling processes including and simultaneously with sideband cooling Figures 2 to 6 The related examples described in the four ion chains can be performed as methods or processes by different devices or systems. Figures 7 to 9BThese methods, processes, apparatus, or systems are further described in additional detail.

[0061] Now refer to Figure 7 , illustrates an example computer device 700 according to aspects of the present disclosure. For example, computer device 700 may represent a single computing device, a plurality of computing devices, or a distributed computing system. Computer device 700 may be configured as a quantum computer (e.g., a quantum information processing (QIP) system), a classical computer, or a combination of quantum and classical computing functions. For example, computer device 700 may be used to process information using quantum algorithms based on trapped ion technology, and may therefore implement methods or processes for efficient cooling, including techniques involving simultaneous or synchronous sideband cooling motion modes. Fig. 9A and Fig. 9B A general example of a computer device 700 as a QIP system that may implement the techniques described herein is illustrated in the example shown in FIG.

[0062] In one example, the computer device 700 may include a processor 710 for performing processing functions associated with one or more features described herein. For example, the processor 710 may be configured to control, coordinate and / or perform various aspects of simultaneous or synchronous sideband cooling motion patterns, and control, coordinate and / or perform various aspects of quantum computing or operations that occur while performing cooling (e.g., collaborative cooling). The processor 710 may include a single or multiple groups of processors or a multi-core processor. In addition, the processor 710 may be implemented as an integrated processing system and / or a distributed processing system. The processor 710 may include a central processing unit (CPU), a quantum processing unit (QPU), a graphics processing unit (GPU), or a combination of these types of processors. In one aspect, the processor 710 may refer to a general-purpose processor of the computer device 700, which may also include additional processors 710 to perform more specific functions.

[0063] In one example, the computer device 700 may include a memory 720 for storing instructions executable by the processor 710 for performing the functions described herein. In one embodiment, for example, the memory 720 may correspond to a computer-readable storage medium storing code or instructions to perform one or more of the functions or operations described herein. In one example, the memory 720 may include instructions for performing the following combined Figure 8 Instructions for various aspects of the described method 800. As with the processor 710, the memory 720 may refer to general memory of the computer device 700, which may also include additional memory 720 to store instructions and / or data for more specific functions.

[0064] In addition, the computer device 700 may include a communication component 730 for establishing and maintaining communications with one or more parties using hardware, software, and services as described herein. The communication component 730 may perform communications between components on the computer device 700 and between the computer device 700 and external devices (e.g., devices located on a communication network and / or devices connected in series or locally to the computer device 700). For example, the communication component 730 may include one or more buses and may further include a transmit chain component and a receive chain component associated with a transmitter and a receiver, respectively, which are operable to interface with external devices.

[0065] In addition, computer device 700 may include data storage 740, which may be any suitable combination of hardware and / or software for mass storage of information, databases, and programs employed in conjunction with the embodiments described herein. For example, data storage 740 may be a data repository for operating system 760 (e.g., a classical OS or a quantum OS). In one embodiment, data storage 740 may include memory 720.

[0066] Computer device 700 may also include user interface component 750, which is operable to receive input from a user of computer device 700, and is also operable to generate output for presenting to the user or providing to different systems (directly or indirectly). User interface component 750 may include one or more input devices, including but not limited to keyboard, numeric keypad, mouse, touch-sensitive display, digitizer, navigation key, function key, microphone, voice recognition component, any other mechanism that can receive input from the user, or any combination thereof. In addition, user interface component 750 may include one or more output devices, including but not limited to display, speaker, tactile feedback mechanism, printer, any other mechanism that can present output to the user, or any combination thereof.

[0067] In one embodiment, the user interface component 750 may send and / or receive messages corresponding to the operation of the operating system 760. In addition, the processor 710 may execute the operating system 760 and / or applications or programs, and the memory 720 or the data storage 740 may store them.

[0068] When the computer device 700 is implemented as part of a cloud-based infrastructure solution, the user interface component 750 may be used to allow a user of the cloud-based infrastructure solution to interact with the computer device 700 remotely.

[0069] Figure 8800 for cooling an ion chain having a plurality of ions according to aspects of the present disclosure. In one aspect, the method 800 may be performed in a computer system (e.g., as part of the operation of a computer system) such as the computer device 700 described above, where, for example, the processor 710, the memory 720, the data storage 740, and / or the operating system 760 may be used to perform or control the functions of the method 800. Similarly, the functions of the method 800 may be performed by, for example, the following in combination Fig. 9A and Fig. 9B The QIP system 900 and its components (eg, the optical controller 920 and its subcomponents) described in greater detail may be implemented or controlled by one or more components of the QIP system.

[0070] At 810 , method 800 includes generating a sideband cooling laser beam for each ion in an ion chain.

[0071] At 820 , method 800 includes simultaneously cooling two or more motional modes associated with ions in the ion chain using respective sideband cooling laser beams until each of the two or more motional modes reaches a motional ground state.

[0072] At 830, method 800 includes performing quantum computation using the ion chain after the two or more modes of motion reach the ground state of motion.

[0073] In another aspect of method 800, simultaneously cooling two or more motion modes includes repeating the following sequence multiple times: resetting the ions to a lower energy state using a re-pumping laser beam; interacting the motion-dependent laser with the generated sideband cooling laser beam to transfer the motion quantum from the lower energy state of the ions to the higher energy state of the ions; and resetting the ions to the lower energy state again. The number of times the sequence is repeated is a predetermined number of times, and the predetermined number of times ensures that all of the two or more motion modes reach a motion ground state. Resetting the ions to a lower energy state using a re-pumping laser beam may include resetting each ion to a lower energy state using a corresponding re-pumping laser beam to achieve asynchronous resetting of the ions.

[0074] In another aspect of method 800, the number of the two or more motion modes is proportional to the number of ions in the ion chain.

[0075] In another aspect of method 800, each of the two or more motion modes has corresponding ions in an ion chain for sideband cooling using a corresponding sideband cooling laser beam.

[0076] In another aspect of method 800, the two or more modes of motion include a longitudinal or axial mode relative to the ion chain, a transverse or radial mode relative to the ion chain, or a combination thereof.

[0077] In another aspect of method 800, the ions in the ion chain include two or more types of ions, one of which is used for cooperative cooling, and simultaneous cooling of the two or more motion modes associated with the ions in the ion chain is performed using ions of the type used for cooperative cooling, and while performing simultaneous cooling, quantum computing is performed using ions of one or more of the remaining types.

[0078] In another aspect of method 800, at least one of the two or more motion modes is sideband cooled using two or more ions and two or more sideband cooling laser beams.

[0079] Fig. 9A is a block diagram illustrating a QIP system 900 according to various aspects of the present disclosure. The QIP system 900 may also be referred to as a quantum computing system, a computer device, a trapped ion quantum computer, etc. In one aspect, the QIP system 900 may correspond to Figure 7 Parts of a quantum computer implementation of computer device 700 in FIG.

[0080] The QIP system 900 may include a source 960 that provides atomic species (e.g., a neutral atom flux) to a chamber 950 having an ion trap 970 that captures atomic species ionized (e.g., photoionized) by an optical controller 920 (e.g., see Fig. 9B ). The light source 930 in the optical controller 920 (e.g., a laser that produces a light beam) may include one or more laser sources that can be used for ionization of atomic species, control of atomic ions (e.g., phase control), fluorescence of atomic ions, which can be monitored and tracked by an image processing algorithm operating in an imaging system 940 in the optical controller 920, and / or perform optical cooling functions described in the present disclosure, including Doppler cooling of motion modes and simultaneous or synchronous sideband cooling. In one aspect, the light source 930 can be implemented separately from the optical controller 920.

[0081] Imaging system 940 may include a high-resolution imager (e.g., a CCD camera) for monitoring atomic ions as they are provided to the ion trap or after they are provided to ion trap 970. In one aspect, imaging system 940 may be implemented separately from optical controller 920, however, using image processing algorithms to detect, identify, and label atomic ions using fluorescence may require coordination with optical controller 920.

[0082] The QIP system 900 may also include an algorithm component 910 that may operate with other portions of the QIP system 900 (not shown) to perform quantum algorithms or quantum operations, including single-qubit operations or multi-qubit operations and extended quantum computations. Thus, the algorithm component 910 may provide instructions to various components of the QIP system 900 (e.g., to the optical controller 920) to enable implementation of the quantum algorithm or quantum operation. In one example, as described above in conjunction with simultaneous or synchronous sideband cooling, if cooperative cooling techniques are being applied, the algorithm component 910 may perform, coordinate, and / or direct the performance of quantum computations or operations after the sideband cooling is complete or during the sideband cooling.

[0083] Fig. 9B At least a portion of an optical controller 920 is shown. In this example, the optical controller 920 may include a beam controller 921, a light source 930, and an imaging system 940. As shown by the dashed lines, one or both of the light source 930 and the imaging system 940 may be implemented separately from the optical controller 920, but communicate with the optical controller 920. The imaging system 940 includes a CCD 941 (or similar imager or camera) and an image processing algorithm component 942. The light source 930 includes a modulator 925 and a plurality of laser sources 935a, ..., 935b, which may be used for one or more of the above functions (e.g., generating a laser or gate beam for a cooling operation).

[0084] The beam controller 921 is configured to perform various aspects described herein for coherently controlling quantum phases on atomic qubits mediated by control fields, such as applied to quantum logic gates, and / or related to generalized interactions between qubits. The beam controller 921 can include a Doppler cooling component 922 configured to use a laser beam to perform a first stage of cooling of a motion mode of an ion chain (e.g., ions in a crystal or lattice in an ion trap 970). The beam controller 921 can also include a sideband cooling component 923 having a simultaneous motion mode cooling component 924 to perform various aspects described herein for a second stage of cooling of a motion mode of an ion chain, wherein the second stage of cooling involves simultaneous or synchronous (e.g., non-sequential) cooling of the motion mode. In one embodiment, the Doppler cooling component 922 and the sideband cooling component 923 can be part of the same component and / or can be implemented separately from the beam controller 921 to communicate with the beam controller 921.

[0085] The various components of the optical controller 920 may operate individually or in combination to perform the various functions described in this disclosure, for example, Figure 8In addition, various components of the optical controller 920 can operate with one or more components of the QIP system 900 to perform various functions described in the present disclosure, such as, Figure 8 Method 800 in.

[0086] Although the present disclosure has been provided according to the illustrated implementations, it will be readily appreciated by those skilled in the art that variations of the embodiments may exist and are within the scope of the present disclosure. Therefore, various modifications may be made by those skilled in the art without departing from the scope of the appended claims.

Claims

1. A method for cooling an ion chain having a plurality of ions, the method comprising: generating a repumping beam configured to simultaneously reset two or more of the plurality of ions in the ion chain; generating a sideband cooling laser beam for each of the two or more ions in the ion chain, wherein each sideband cooling laser beam has a different frequency to cool a different motion mode with the corresponding ion; simultaneously cooling two or more motion modes associated with the two or more ions in the ion chain using respective sideband cooling laser beams and the respective ions until each of the two or more motion modes reaches a motion ground state; as well as After the two or more motion modes reach the motion ground state, quantum computing is performed using the ion chain.

2. The method of claim 1, wherein simultaneously cooling two or more motion patterns comprises repeating the following sequence a plurality of times: resetting the two or more ions simultaneously to a lower energy state using a repumping laser beam based on the generated repumping beam; causing a motion-dependent laser to interact with the generated sideband cooling laser beam to transfer motional quanta from the lower energy state of the two or more ions to a higher energy state of the two or more ions; as well as Based on the generated repumping beam, the two or more ions are reset to the lower energy state again simultaneously. 3 . The method according to claim 2 , wherein the sequence is repeated a predetermined number of times, the predetermined number of times ensuring that all of the two or more motion patterns reach the motion base state. The method of claim 1 , wherein the number of the two or more motion modes is proportional to the number of the plurality of ions in the ion chain.

5. The method of claim 1, wherein the two or more motion modes include a longitudinal or axial mode relative to the ion chain, a transverse or radial mode relative to the ion chain, or a combination thereof.

6. The method according to claim 1, wherein: The two or more ions in the ion chain include two or more species of ions, wherein one species of ions of the two or more species is used for cooperative cooling, performing simultaneous cooling of the two or more motion modes associated with the two or more ions in the ion chain using the one species of ions for cooperative cooling, and While the simultaneous cooling is being performed, the quantum computation is performed using ions of one or more of the remaining species of the two or more species.

7. A quantum information processing (QIP) system for cooling an ion chain having a plurality of ions, the system comprising: one or more light sources configured to: generate a repumping beam configured to simultaneously reset two or more of the plurality of ions in the ion chain; and generate a sideband cooling laser beam for each of the two or more ions in the ion chain, wherein each sideband cooling laser beam has a different frequency to cool a different motion mode with a corresponding ion; a beam controller configured to simultaneously cool two or more motion modes associated with the two or more ions in the ion chain using respective sideband cooling laser beams and the respective ions until each of the two or more motion modes reaches a motion ground state; as well as An algorithm component is configured to perform quantum computation using the ion chain after the two or more motion modes reach the motion ground state.

8. The quantum information processing (QIP) system of claim 7, wherein the beam controller configured to cool two or more motion modes simultaneously is further configured to repeat the following sequence multiple times: resetting the two or more ions simultaneously to a lower energy state using a repumping laser beam based on the generated repumping beam; causing a motion-dependent laser to interact with the generated sideband cooling laser beam to transfer motional quanta from the lower energy state of the two or more ions to a higher energy state of the two or more ions; as well as Based on the generated repumping beam, the two or more ions are reset to the lower energy state again simultaneously.

9. The quantum information processing (QIP) system according to claim 8, wherein the sequence is repeated a predetermined number of times, the predetermined number of times ensuring that all of the two or more motion modes reach the motion ground state.

10. The quantum information processing (QIP) system of claim 7, wherein the number of the two or more motion modes is proportional to the number of the plurality of ions in the ion chain.

11. The quantum information processing (QIP) system of claim 7, wherein the two or more motion modes include a longitudinal or axial mode relative to the ion chain, a transverse or radial mode relative to the ion chain, or a combination thereof.

12. The quantum information processing (QIP) system according to claim 7, wherein: The two or more ions in the ion chain include two or more species of ions, wherein one species of ions of the two or more species is used for cooperative cooling, The beam controller is configured to simultaneously cool the two or more motion modes associated with the two or more ions in the ion chain by using the one species of ions for cooperative cooling, and The algorithm component is configured to perform the quantum computation using ions of one or more of the remaining ones of the two or more species while performing the simultaneous cooling.

13. A quantum information processing (QIP) device for cooling an ion chain having a plurality of ions, the device comprising: means for generating a repumping beam configured to simultaneously reset two or more ions in the ion chain; means for generating a sideband cooling laser beam for each of the two or more ions in the ion chain, each sideband cooling laser beam having a different frequency to cool a different motion mode with the corresponding ion; means for simultaneously cooling two or more motion modes associated with said two or more ions in said ion chain using respective sideband cooling laser beams and said respective ions until each of said two or more motion modes reaches a ground state of motion; as well as Means for performing quantum computation using the ion chain after the two or more motion modes reach the motion ground state.

14. The quantum information processing (QIP) device according to claim 13, wherein: The two or more ions in the ion chain include two or more species of ions, wherein one species of ions of the two or more species is used for cooperative cooling, using the one species of ions for cooperative cooling to simultaneously cool the two or more motion modes associated with the two or more ions in the ion chain, and While the simultaneous cooling is being performed, the quantum computation is performed using ions of one or more of the remaining species of the two or more species.

15. A computer readable storage medium storing code having instructions executable by a processor for cooling an ion chain having a plurality of ions, the code comprising: code for generating a repumping beam configured to simultaneously reset two or more ions in the ion chain; code for generating a sideband cooling laser beam for each of the two or more ions in the ion chain, each sideband cooling laser beam having a different frequency to cool a different motion mode with the corresponding ion; code for simultaneously cooling two or more motion modes associated with the two or more ions in the ion chain using respective sideband cooling laser beams and the respective ions until each of the two or more motion modes reaches a motion ground state; as well as Code for performing quantum computation using the ion chain after the two or more motion modes reach the motion ground state.

16. The computer-readable storage medium of claim 15, wherein: The two or more ions in the ion chain include two or more species of ions, wherein one species of ions of the two or more species is used for cooperative cooling, using the one species of ions for cooperative cooling to simultaneously cool the two or more motion modes associated with the two or more ions in the ion chain, and While the simultaneous cooling is being performed, the quantum computation is performed using ions of one or more of the remaining species of the two or more species.

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