Data readout from quantum computing systems

Abstract

An imaging device for a quantum computing system is arranged to capture an image frame of a grid by detecting photons. Quantum devices, e.g. qubits, are arranged in a grid of cells, wherein the grid i

Description

Field of the Invention

[0001] The present invention relates generally to quantum computing systems, more specifically to methods, circuitry, systems, and computer-readable media for reading data from a quantum computing system. Background

[0002] Quantum computing systems, often referred to as quantum computers, utilise quantum mechanical phenomena to perform computational tasks. Quantum computing systems are formed of many quantum devices, for example qubits, which may be operated on by quantum gates to manipulate the state of the qubit to perform a particular calculation.

[0003] There are many different types of quantum computing system, where these are usually distinguished from one another by the form of the quantum device making up the quantum computing system. Data may be read from these quantum computing systems in various ways, for example depending on the type of quantum computing system. Generally, however, quantum computing systems are susceptible to errors in the data which may be read from them. Summary of the Invention

[0004] The invention is defined by the appended claims.

[0005] According to a first aspect, there is provided a computer-implemented method for reading data from a quantum computing system comprising a plurality of quantum devices arranged in a grid of cells, wherein the grid of cells comprises a plurality of rows of cells, wherein each cell of the grid of cells corresponds to a possible quantum device location, wherein each quantum device of the quantum computing system is configured to emit photons in response to a stimulus according to a state of the quantum device, and wherein the quantum computing system comprises an imaging device configured to capture a plurality of image frames of the grid of cells. The method comprises: for each of the plurality of image frames of the grid of cells: identifying one or more pertinent cells of the grid of cells for the image frame; identifying one or more regions of interest in the image frame, wherein each region of interest corresponds to a respective pertinent cell, and wherein each region of interest comprises one or more pixels of a plurality of pixels of the image frame; for a plurality of sets of pixels making up the image frame, wherein each of the sets of pixels comprises one or more rows of pixels: receiving, from the imaging device, image data for the set of pixels of the image frame, the set of pixels corresponding to a row of cells of the plurality of rows of cells, wherein the image data is indicative of a number of photons received at each pixel in the set of pixels, converting the image data into reduced image data, the reduced image data comprising image data only for pixels of the set of pixels within the one or more regions of interest, and determining, based on the reduced image data, state information for one or more pertinent cells in the row of cells.

[0006] As such, for quantum computing systems in which quantum devices emit one or more photons in response to a stimulus according to a state of the quantum device, image data from an image device may be used to determine the state of particular quantum devices for which measurement data is desired. According to the present disclosure, only those pixels of the image data relevant to the cells containing the quantum devices of interest are analysed in order to determine the state information. As such, the quantity of image data that is processed per image frame is significantly reduced, meaning that the relevant state information from each image frame may be processed more quickly, for example in real-time (i.e. at least at the rate the image data 1 is received). Rapid processing of image data for such quantum computing systems is particularly important for identifying and correcting errors in quantum computing systems, as error correction must be performed in real-time in order to prevent accumulation of a data backlog, which would ultimately slow down the operation of the quantum computing system.

[0007] A quantum computing system may refer generally to any system formed of quantum devices which may be used for quantum computation. The quantum computing system may include the quantum devices themselves and may in some cases be considered to include additional components, such as a controller for the quantum computing system and / or hardware for manipulating the quantum devices (i.e. applying quantum gates to the quantum devices). Quantum devices refer generally to a system which implements one or more units of quantum information. The quantum device may be, for example a qubit, or any other unit of quantum information such as a qutrit or qudit, and could be realised in a number of different ways, such as using a Rydberg atom. A pertinent cell is a cell for which a readout of the quantum device within said cell is desired. As such, a pertinent cell may equally be referred to as a cell of interest, or any other suitable name. A region of interest refers to one or more regions of the image frame corresponding to the pertinent cells. The grid of cells may otherwise be referred to as a lattice.

[0008] Image data is indicative of a number of photons received at a particular pixel, however the image data may take many forms. For example, the image data may include a count of the number of photons at each pixel, or the image data may include a relative brightness of each pixel, where the relative brightness is correlated with the number of photons received. State information for a cell may include an occupancy of a cell (i.e. whether a quantum device is present within that cell) and / or a state of a quantum device within the cell. The state information may in some cases additionally include so-called ‘soft’ information, for example indicating a probability / confidence of the occupancy / state of the cell / quantum device.

[0009] Advantageously, converting the image data into reduced image data may comprise discarding the image data for pixels of the set of pixels outside the one or more regions of interest. As such, overall memory usage for methods according to the present disclosure may be reduced.

[0010] According to some examples, the set of pixels corresponding to the row of cells comprises a plurality of rows of pixels, wherein receiving the image data comprises sequentially receiving image data for each of the plurality of rows of pixels, wherein converting the image data into reduced image data comprises, upon receiving the image data for a respective row of pixels, converting the image data for the respective row of pixels into reduced image data for the respective row of pixels, and wherein determining the state information for the one or more pertinent cells is based on the reduced image data for each of the rows of pixels of the set of pixels. In other words, reduced image data is determined for each pixel row as it is received, for example rather than waiting for each row of pixels associated with a particular row of cells to be received. As such, the reduced image data can be generated in real-time, thereby improving data readout speed. Moreover, in some cases, state information for a particular row of cells may be determined based on determining that reduced image data for all rows of pixels associated with the particular row of cells has been determined. As such, state information can be determined as early as possible in the readout process, thereby improving data readout speed.

[0011] In some cases, the state information for the one or more pertinent cells comprises information regarding an occupancy of the respective pertinent cell. In other words, the state information may indicate whether a particular cell is occupied by a quantum device or is unoccupied. Accordingly, locations and distribution of quantum devices within the quantum computing system may be readily determined.

[0012] In some examples, the state information for the one or more pertinent cells comprises information regarding a state of a quantum device within the respective pertinent cell. As such, data may be read from specific quantum devices of the quantum computing system.

[0013] Advantageously, the information regarding the state of a quantum device may comprise an indication of the state of the quantum device and a certainty value for the state of the quantum device. As such, so-called ‘soft’ state information may be readily read from the quantum computing system. Further advantageously, the information regarding the state of the quantum device may be provided as a single value for each quantum device, thereby providing minimising memory usage.

[0014] In some cases, the one or more pertinent cells for a first image frame are different to the one or more pertinent cells for a second image frame. Accordingly, it is possible to easily obtain state information for different cells / quantum devices at different times in a fast and efficient manner.

[0015] According to certain examples, identifying the one or more pertinent cells includes receiving, from a controller of the quantum computing system, an indication of the one or more pertinent cells for the image frame. As such, the pertinent cells may be determined based on the operation of the quantum computing system (e.g. based on a quantum circuit being executed on the quantum computing system and / or based on the cells stimulated by the quantum computing system).

[0016] In some cases, identifying the one or more pertinent cells comprises identifying respective co-ordinates in the grid of cells for the one or more pertinent cells. As such, the pertinent cells may be identified in a fast and efficient manner.

[0017] Advantageously, identifying the one or more regions of interest in the image frame may be based on a predetermined mapping between the grid of cells and co-ordinates of the pixels of the image frame. Accordingly, the pixels for which image data should be kept for inclusion in the reduced image data may be quickly identified, thereby improving readout speed for the quantum computing system.

[0018] In some cases, the one or more pertinent cells include one or more cells comprising a syndrome quantum device. Accordingly, data indicative of errors in quantum devices may be read from the quantum computing system in real-time.

[0019] According to certain examples, each set of pixels comprises a plurality of rows of pixels, wherein the plurality of rows of pixels correspond to the row of cells. In other words, each row of cells may associated with a plurality of rows of pixels. The reduced image data for these plurality of rows of pixels may then be used to determine the state information for the row of cells.

[0020] In certain examples, the quantum computing system is a neutral-atom quantum computing system. However, it should be appreciated that in general the techniques of the present disclosure are suitable for any quantum computing system in which data is read from the quantum devices using an imaging device (whether optical, infrared, ultraviolet, or any other suitable form of imaging device).

[0021] In some cases, the quantum devices are qubits, however it should be appreciated that the techniques of the present disclosure are suitable for any form of quantum device where the state of said quantum device can be determined using an imaging device (whether optical, infrared, ultraviolet, or any other suitable form of imaging device).

[0022] According to a second aspect of the disclosure, there is provided a computer-implemented method for identifying errors in a quantum computing system, the method comprising: the method as described herein; and wherein the method further comprises: identifying, based on the state information, syndrome data indicative of one or more errors in the state of one of more quantum devices in the grid of cells. As such, errors in quantum devices of the quantum computing system may be identified in real-time.

[0023] In some case, identifying the syndrome data is based on a comparison of the state information for two or more image frames. As the image data for each image frame can be processed quickly according to the present disclosure, state information for each image frame can therefore be determined quickly, and syndrome data identified in real-time.

[0024] Advantageously, the method may further comprise: determining, based on the syndrome data, a correction for an error state of one or more data quantum devices within the grid of cells. As such, errors within a quantum computing system may be identified quickly, thereby facilitating real-time and large-scale error correction in quantum computing systems. The method may optionally further comprise obtaining a logical state measurement of a logical state encoded in the one or more data quantum devices and applying the correction to the logical state measurement.

[0025] According to a third aspect of the invention, there is provided: circuitry for reading data from a quantum computing system comprising a plurality of quantum devices arranged in a grid of cells, wherein the grid of cells comprises a plurality of rows of cells, wherein each cell of the grid of cells corresponds to a possible quantum device location, wherein each quantum device of the quantum computing system is configured to emit photons in response to a stimulus according to a state of the quantum device, and wherein the quantum computing system comprises an imaging device configured to capture a plurality of image frames of the grid of cells, wherein the circuitry is configured to execute the method as described herein.

[0026] According to a fourth aspect of the invention, there is provided a system comprising: the circuitry as described herein; and the imaging device.

[0027] According to a fifth aspect of the invention, there is provided a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method as described herein. Brief Description of the Drawings

[0028] Embodiments of the invention will now be described, by way of example only, with reference to the following figures.

[0029] In accordance with one (or more) embodiments of the present invention the figures show the following:

[0030] Figure 1 illustrates a set of cells and quantum devices of a quantum computing system from which state information can be read using an imaging device.

[0031] Figure 2 illustrates the manner in which quantum devices of a row of cells of the quantum computing system may be imaged.

[0032] Figure 3 illustrates a system including a readout apparatus according to the present disclosure.

[0033] Figure 4 illustrates an image frame including regions of interest according to the present disclosure.

[0034] Figure 5 illustrates the generation of reduced image data for a row of cells according to the present disclosure.

[0035] Figure 6 illustrates reduced image data for an image frame, according to the present disclosure.

[0036] Figure 7 illustrates a flow chart depicting a method for reading data from a quantum computing system according to the present disclosure.

[0037] Figure 8 illustrates a readout apparatus or circuitry according to the present disclosure.

[0038] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[0039] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future. Detailed Description

[0040] As the field of quantum computing matures, various quantum computing systems are under active development. Data may be read from these different quantum computing systems using various techniques, based on the technology used in the quantum computing system. For example, some quantum computing technologies allow data to read from the quantum computing system using images of the quantum devices (e.g. qubits) themselves. Neutral atom quantum computing systems are just one example of such a quantum computing technology, however other types of quantum computing system may operate in this way. Neutral atom quantum computing systems utilise qubits in the form of neutral Rydberg atoms. Rydberg atoms have multiple stable states, corresponding to the |0) and |1) states of a qubit, and may be confined to a particular location using optical tweezers (or any other suitable confinement technology). Furthermore, the state of the Rydberg atoms may be manipulated using laser pulses, thereby implementing quantum gates. Accordingly, Rydberg atoms are capable of functioning as qubits (or potentially other quantum devices), and may be equally referred to as qubits hereinafter.

[0041] For neutral atom quantum computing systems (and potentially other types of quantum computing system), the qubits may be arranged in a grid (i.e. lattice) comprising a plurality of rows of cells, where each cell is a possible location for a qubit. That is, there may be a finite number of predetermined locations at which quantum devices may be located, where the possible locations may be referred to as cells, where the locations are arranged in a grid. This arrangement of cells is illustrated in Figure 1. Figure 1 shows a grid 100 of cells 110, where the grid 100 contains a plurality of rows 120(1)-(4) of cells, and each cell 110 is a possible location for a qubit 130. As can be seen in Figure 1, some cells 110 may contain a qubit 130, while other cells 110 may not contain a qubit 130. Generally, qubits 130 may be relocated within the grid 100 such that the occupancy of a cell 110 (i.e. whether the cell 110 contains a qubit 130) may change. It should be noted the arrangement of quantum devices shown in Figure 1 and discussed herein may be used for other types of quantum computing system.

[0042] For at least neutral atom quantum computing systems, the qubits 130 may exhibit fluorescence, such that the qubits 130 may emit photons in response to a particular stimulus. The stimulus may, for example, be a laser pulse or other source of electromagnetic radiation. The degree of fluorescence, i.e. the amount of photons emitted by each qubit 130, depends on the state of the qubit 130. That is, qubits 130 in state |0) emit a different quantity / rate of photons than qubits 130 in the |1) state. Accordingly, the state of a qubit 130 in the grid 100 may be determined by measuring the quantity of photons emitted by a particular qubit 130. It should be appreciated that the techniques are in general applicable to any quantum computing system where the quantum devices emit photons according to the state of the quantum device.

[0043] The state of qubits 130 in a quantum computing system can therefore be measured by taking an image of the grid 100 of cells 110. Imaging devices generally capture images by collecting photons at a plurality of sensor elements corresponding to a plurality of pixels. The qubits 130 may emit photons of varying wavelength, and as such the imaging device may be configured to detect photons of a variety of wavelengths, such as optical, infra-red, ultraviolet and / or any other suitable wavelength of photon, according to the photon wavelengths emitted by the qubits 130. The imaging device has an exposure length, which is a duration over which photons are collected for a single image at the sensor elements (referred to as pixels hereinafter for brevity). As such, an imaging device may be arranged to capture an image of the grid 100 by detecting photons, where each of the detected photons is assigned to a particular pixel. Accordingly, a quantity of photons received at each pixel can be determined, from which a final image is produced. Figure 2 illustrates an example of this arrangement for the first row 120(1) of the grid, where the first row 120(1) contains cells 110a-d, and wherein cells 110a-c each contain a qubit 130, but cell 110d does not contain a qubit. The group of pixels 210 associated with the first row of cells 120(1) includes four rows of pixels 220(1)-(4).

[0044] The cells 110a-d may be provided with a stimulus such that qubits 130 within the cells 110a-d emit photons according to the state of the qubit 130. As such, the qubits 130 in cells 110a-c will emit photons at a particular rate / amount based on the state of the qubit 130. That is, qubits 130 in the |0) state emit a different quantity / rate of photons than qubits 130 in the |1) state, and as such different numbers of photons will be detected from qubits in different states in a single exposure corresponding to a single image frame. No photons will be emitted from cell 110d as no qubit 130 is present, and as such no photons (or only a small number of photons indistinguishable from noise / background levels) will be detected from cell 110d in the exposure corresponding to the image frame. As such, no photons (or only background levels of photons) will be detected at pixels 210 (or rather sensor elements of the imaging device associated with pixels) associated with cell 110d. Moreover, as can be seen from Figure 2, a number of pixels may sufficiently distant from any cells 110 such that no photons (or only background levels of photons) are likely to be detected at said pixels 210, regardless of the photon emission from the cells 110. For example, the pixels 210 between each of the cells 110 and the pixels in the first row of pixels 220(1) and the fourth row of pixels 220(4) are sufficiently distant from any cells 110 in the first row 120(1) that 6 the output of said pixels 210 is unlikely to provide a useful indication of the occupancy of a cell 110 or the state of a qubit 130.

[0045] Imaging devices generally output image data sequentially in rows of pixels 220. For example, in the context of Figure 2, the imaging device may output image data (indicative of a number of photons associated (i.e. received) at each pixel 210) for the first row of pixels 220(1) at a first time, output image data for the second row of pixels 220(2) at a second time, output image data for the third row of pixels 220(3) at a third time, and output image data for the fourth row of pixels 220(4) at a fourth time, where the second time is after the first time, the third time is after the second time, and the fourth time is after the third time. The image data for each pixel 210 in a row 220 may be output collectively. In other words, the image data for the pixels 210 is output by the imaging device sequentially row-by-row of pixels. However, as discussed above, much of this image data may not be useful for determining the occupancy of a cell 110 or the state of a qubit 130.

[0046] In some cases it may be desirable to determine an occupancy of each of the cells 110 in the grid 100, and / or the state of each of the qubits 130 within the grid 100, for example to determine the occupancy of the cells 110 in an initial set-up phase of operation of the quantum computing system. As such, each cell 110 within the grid 130 may be provided with a stimulus. Conversely in some cases it may only be desirable to determine the occupancy / state of a subset of the cells 110 / qubits 130 in the grid 100. For example, it should be appreciated that in neutral atom quantum computing systems (and indeed other quantum computing systems) the cells / qubits may be selectively stimulated. In other words, in some cases only a selected subset of the cells 110 may be provided with a stimulus, such that only qubits 130 in those selected cells 110 emit photons. As such, it may only be desirable / necessary to determine the occupancy / state of the qubits / cells which are provided with a stimulus. Moreover, even in cases where each of the cells 110 in the grid 100 are provided with a stimulus, it may still only be desirable to determine the occupancy / state of a subset of the cells / qubits within the grid 100. As such, in many cases the image data for a subset of the pixels may not be useful, as it is not desirable to know the state information (i.e. occupancy of a cell or state of a qubit) for cells associated with those pixels.

[0047] Therefore, as can be seen from the foregoing discussion, there are a number of instances in which image data for a subset of the pixels 210 in an image frame may not be necessary for determining desired image data for cells 110 in the grid 100. Processing this unwanted image data may consume significant processing resources and therefore slow down or delay processing of image data for the cells of interest. This can delay the identification and correction of errors in the quantum computing system, which slows the operation of the quantum computing system as a whole.

[0048] Therefore according to the present disclosure there is provided a computer-implemented method for reading data from a quantum computing system comprising a plurality of quantum devices arranged in a grid of cells, wherein the grid of cells comprises a plurality of rows of cells, wherein each cell of the grid of cells corresponds to a possible quantum device location, wherein each quantum device of the quantum computing system is configured to emit photons in response to a stimulus according to a state of the quantum device, and wherein the quantum computing system comprises an imaging device configured to capture a plurality of image frames of the grid of cells. The method comprises: for each of the plurality of image frames of the grid of cells: identifying one or more pertinent cells of the grid of cells for the image frame; identifying one or more regions of interest in the image frame, wherein each region of interest corresponds to a respective pertinent cell, and wherein each region of interest comprises one or more pixels of a plurality of pixels of the image frame; for a plurality of sets of pixels making up the image frame, wherein each of the sets of pixels comprises one or more rows of pixels: receiving, from the imaging device, image data for the set of pixels of the image frame, the set of pixels corresponding to a row of cells of the plurality of rows of cells, wherein the image data is indicative of a number of photons received at each pixel in the set of pixels, converting the image data into reduced image data, the reduced image data comprising image data only for pixels of the set of pixels within the one or more regions of interest, and determining, based on the reduced image data, state information for one or more pertinent cells in the row of cells.

[0049] Figure 3 shows an example system according to the present disclosure. The system includes a quantum computing system 300 comprising a plurality of quantum devices 350 (e.g. qubits 130 arranged in grid 100), an imaging device (i.e. camera) 320 for detecting photons emitted from the quantum devices 350, qubit (or other quantum device) manipulation hardware 340 for manipulating the quantum devices 350, and a controller 330 for controlling the imaging device and the qubit manipulation hardware 340 of the quantum computing system 300. The system further includes a readout apparatus 310 according to the present disclosure. The readout apparatus 310 may be considered to be separate from the quantum computing system 300 (as shown in Figure 3), or the readout apparatus 310 may be considered to be part of the quantum computing system 300. The readout apparatus 310 may be considered to include various logical modules, which may be implemented by common processors and memories, or may each be implemented by separate processors and memories. The readout apparatus 310 may include a buffer 311, a mapper module 312, a discrimination module 313, a state module 314, and may additionally include a syndrome module 315, and a correction module 316, each of which will be discussed in more detail below, which may all be considered in some cases to be logically distinct from one another. The readout apparatus may be implemented on a conventional computing apparatus, one or more field-programmable gate arrays (FPGAs), or one or more applicationspecific integrated circuits (ASICs).

[0050] The controller 330 may include various logical modules, such as a imaging device (i.e. camera) controller 331 configured to control the imaging device 320 (for example, by setting an exposure length and / or setting a timing for image capture), a cell identification module 332, and a hardware control module 333 configured to control the manipulation hardware 340 (and optionally other hardware of the quantum computing system 300). The manipulation hardware 340 may include hardware for stimulating cells (and therefore quantum devices 350) within the quantum computing system 300 (e.g. by emitting laser pulses towards particular cells). The manipulation hardware 340 may in some cases include hardware for altering the state of a quantum device 350 (i.e. applying one or more quantum gates to a quantum device 350), such as by emitting specific laser pulses towards particular quantum devices 350. Alternatively, hardware for altering the state of a quantum device 350 may be considered to be separate from the qubit manipulation hardware 340. Furthermore, in some cases, the qubit manipulation hardware 340 may include hardware for moving one or more quantum devices 350 between different cells. Alternatively, hardware for moving one or more quantum devices 350 between different cells may be considered to be separate from the qubit manipulation hardware 340.

[0051] Figure 4 illustrates an example process for reading data from a quantum computing system according to the present disclosure, where the grid 100 of cells 110 is identical to that shown in Figure 1. In the case of Figure 4, state information for only the subset 115 of cells 110 is desired for a particular image frame 200. It should be noted that the pertinent cells 115(1)-(4) (i.e. the cells 110 for which image data is desired or required) is determined in advance of receiving the image data 200 for the image frame 200. Furthermore, the pertinent cells 115 may 8 be different for each image frame 200. The cell identification module 332 of the controller 330 of the quantum computing system 300 may determine the pertinent cells 115 for each image frame and may indicate the pertinent cells 115 for one or more image frames to the readout apparatus 310. The pertinent cells 115 for an image frame may be determined by the cell identification module 332 according to a user input or autonomously, for example based on a quantum algorithm (i.e. quantum circuit) to be executed by the quantum computing system 300. The hardware control module 330 may control the qubit manipulation hardware 340 to cause the qubit manipulation hardware module 340 to stimulate one or more of the quantum devices 350. For example, the hardware control module 333 may control the qubit manipulation hardware 340 to cause the qubit manipulation hardware 340 to stimulate only the pertinent cells 115 determined by the cell identification module 332. Furthermore, the camera controller 331 may control the camera 320 to capture one or more image frames (i.e. image data for one or more image frames) of the quantum devices 350 of the quantum computing system 300.

[0052] The cell identification module 332 may indicate the pertinent cells 115 to the readout apparatus 310 in advance of the transmission of the image data by the camera 320. This can be done e.g. by indicating a co-ordinate (i.e. identifier) of each of the pertinent cells 115. Upon identifying the pertinent cells 115(1)-(4) for the image frame 200, the mapper module 312 of the readout apparatus 310 may identify a region of interest 230 corresponding to the pertinent cells 115. For example, each of the pertinent cells 115(1)-(4) may have its own associated region of interest 230(1)-(4), where each region of interest 230 comprises one or more pixels of the image frame 200 corresponding to the respective pertinent cell 115. In other words, the pixels (i.e. region(s) of interest 230) relevant for determining the state information for the pertinent cells 115 are identified. The region of interest 230 may be a single contiguous region of interest or a plurality of discrete regions of interest. It should be noted that the identification of the region(s) of interest 230 may be performed prior to receiving the image data from the imaging device. For example, the co-ordinates (i.e. identifiers) of the pixels in the regions of interest 230 may be identified based on the identification of the pertinent cells 115 and a predefined mapping between the pixels of the image data and the cells 110 of the grid 100 (e.g. based on a prior calibration).

[0053] Figure 5 illustrates a close-up view of the first row of cells 120(1) and the regions of interest 230 associated with cells in the row 120(1). In particular, the first row of cells 120(1) includes a first pertinent cell 115(1) and a second pertinent cell 115(2). The first pertinent cell 115(1) has an associated region of interest 230(1) comprising one or more pixels (in this case four pixels), and the second pertinent cell 115(2) has an associated region of interest 230(2) comprising one or more pixels. The image data is received by the readout apparatus 310 from the imaging device 320 row-by-row of pixels, and is stored in buffer 311. The image data may, for example, include a count of the number of photons at each pixel, or the image data may include a relative brightness of each pixel, where the relative brightness is correlated with the number of photons received. According to the present disclosure, upon receiving the image data for a particular row of pixels 220, the image data may be converted into reduced image data which comprises only image data for pixels within the region(s) of interest 230. The image data stored in the buffer 311 may be converted to the reduced image data by the discrimination module 313. For example, in order to obtain the reduced image data, the image data for pixels outside of the region(s) of interest 230 may be discarded. The image data may optionally be discarded before being stored in the buffer 311. In Figure 5, image data for pixels outside of the region(s) of interest 230 is shaded.

[0054] In the example of Figure 5, upon receiving image data for the first row of pixels 220(1), the discrimination module 313 may determine that none of the pixels in the first row 220(1) are within the region(s) of interest 230, and as such image data for these pixels is not included in the 9 reduced image data, and may be discarded. Upon receiving image data for the second row of pixels 220(2), the discrimination module 313 may determine that two pixels are within region of interest 230(1) and two pixels are within region of interest 230(2). As such, image data for these pixels is included within the reduced image data, and image data for the remaining pixels in the second row 220(2) is not included within the reduced image data and may be discarded. Similarly, upon receiving image data for the third row of pixels 220(3), the discrimination module 313 may determine that two pixels are within region of interest 230(1) and two pixels are within region of interest 230(2), and as such image data only for these pixels in the second row 220(3) are included within the reduced image data. Furthermore, image data for pixels in the fourth row 220(4) may not be included in the reduced image data, as no pixels in the fourth row 220(4) are within the region(s) of interest 230.

[0055] This process may be repeated by the discrimination module 313 for each of the rows of pixels 220 in the image frame 200. As such, reduced image data for the image frame may be determined which includes image data only for pixels within the region(s) of interest 230(1)-(4), as shown in Figure 6, where image data for pixels outside of the regions of interest 230(1)-(4) and therefore not included within the reduced image data is shaded. The reduced image data therefore provides an indication of a number of photons received at each pixel within the regions of interest 230(1)-(4). Based on this image data, state module 314 may determine a total number of photons received from each pertinent cell 115(1)-(4) (i.e. from each region of interest 230(1)-(4)). For example, the total number of photons received from each pixel in a particular region of interest 230 may be summed together to determine a total number of photons received from that region of interest. The state module may therefore determine an indication of a total number of photons received from each pertinent cell 115(1)-(4), for example using the mapping between the regions of interest 230 and the cells 110 of the grid 100.

[0056] Based on the indication of the total number of photons received from each pertinent cell 115(1)-(4), the state module 314 may determine state information of the pertinent cells 115(1)-(4). As previously mentioned, this can include, for example, an occupancy of the cell (i.e. whether a qubit or other quantum device is present within the cell) and / or a state of a qubit (or other quantum device) within the cell. For example, each of the pertinent cells 115(1), 115(3), 115(4) contains a qubit 130 and as such the number of photons received from these pertinent cells 115(1), 115(3), 115(4) will be above a background noise level (i.e. above a predetermined threshold), such that the image data for these cells 115(1), 115(3), 115(4) indicates that they are occupied. Accordingly, the determined state information may include an indication that pertinent cells 115(1), 115(3), 115(4) are occupied by a qubit 130. Conversely, pertinent cell 115(2) does not contain a qubit 130 and as such the number of photons received from pertinent cell 115(2) will be indistinguishable from a background noise level (i.e. below a predetermined threshold), such that the image data for this cells 115(2) indicates that it is unoccupied. Accordingly, the determined state information may include an indication that pertinent cell 115(2) is unoccupied. Furthermore, in some cases, a cell might be occupied by more than one quantum device 130. Accordingly, in some cases the state information may either indicate whether the cell is occupied or unoccupied, or the state information may indicate whether the cell is unoccupied, occupied by one quantum device, or occupied by more than one quantum device.

[0057] In addition to determining the occupancy of the pertinent cells 115, the state information may additionally or alternatively indicate a state of qubits 130 within the pertinent cells 115. In other words, the state information may indicate whether a qubit is in a |0) state or a |1) state. For example, based on the number of photons received for a pertinent cell 115 being within a first range (i.e. above a first threshold (i.e. an occupancy threshold) but below a second threshold), 10 the state module 314 may determine that the qubit 130 for that pertinent cell 115 is in a first state. Conversely, based on the number of photons received for a pertinent cell 115 being within a second range (i.e. above the second threshold), the state module 314 may determine that the qubit 130 for that pertinent cell 115 is in a second state. Additional ranges may be defined for other types of quantum device, for example, three photon ranges may be defined for qutrits. Alternatively, the state may be determined based on a detected photon wavelength.

[0058] Therefore, according to the present disclosure, the readout apparatus 310 may perform real-time state determination for quantum devices 350 within a quantum computing system 300. The state information may include an indication of the occupancy of the cell and / or a state of a qubit in a cell. Moreover, the state information may in some cases include so-called ‘soft’ information, for example indicating a probability or certainty of the state information. For example, the soft information may indicate a certainty value that a cell is occupied or unoccupied, or a certainty value that a qubit is in a |0) state or a |1) state. Moreover, in some cases, the state information for each cell may be in the form of a single value between two limit values, where the limit values indicate 100% certainty for the state information. As just one example, the state information may be given as a value from 0 to 255, where 0 represents a qubit having a |0) state with 100% certainty and where 255 represents a qubit having a |1) state with 100% certainty, where intermediate values indicate |0) or |1) states with certainty values based on how close the value is to 0 or 255. It should be appreciated that a 256 bin (8 bit) scale is just one example scale and that different scales may be used, for example based on the hardware / memory design of the readout apparatus 310. Furthermore, while the above example describes the use of a scale for the state of a qubit, the same type of scale may be used for occupancy. Furthermore, a scale having three limit values may be used to represent occupancy and qubit state information. For example, a scale from 0 to 200 may be used, where 0 represents an unoccupied cell with 100% certainty, 100 represents a cell having a qubit in state |0) (in this example state |0) has a lower fluorescence than state 11)) with 100% certainty, and 200 represents a qubit in state |1) with 100% certainty. Moreover, in cases where the quantum devices are qutrits or qudits, a scale including a number of limit values corresponding to the number of possible states (or the number of possible states plus 1 if occupancy information is desired) may be used.

[0059] It should be appreciated that the state information for the pertinent cells 115 may be determined by the state module 314 once the reduced image data for the entire image frame 200 has been determined (and after the image data for the entire image frame has been received). However, in other cases, the state module 314 may determine the state information for a particular pertinent cell 115 (or subset of the pertinent cells 115) before the reduced image data for the entire image frame 200 has been determined (and before the image data for the entire image frame 200 has been received). For example, upon determining that image data has been received for each pixel within a particular pertinent cell 115, and that reduced image data has been generated (i.e. determined) for that particular pertinent cell 115, the state information for that particular pertinent cell 115 may be determined by the state module 314.

[0060] In some cases, the readout apparatus 310 may include a syndrome module 215 configured to identify syndrome data which is indicative of one or more errors in the state of one or more quantum devices 350 in one or more image frames. For example, the pertinent cells 115 may include one or more syndrome (e.g. ancilla) qubits which may indicate the presence of a bit flip or phase flip in the state of one or more data qubits. The syndrome module 315 may therefore determine one or more qubits (or cells) at which an error has occurred. As such, as well as realtime state determination, the readout apparatus 310 may perform real-time syndrome / error identification.

[0061] In addition, in some examples the readout apparatus 310 may include a correction module 316 configured to determine, based on the syndrome data determined by the syndrome module 315, correction data indicating a correction to the state of one or more quantum devices 350. For example, the correction module 316 may determine that the state of a particular qubit should be flipped from |0) to 11), or vice versa. The readout apparatus 310 may, in some cases, transmit the correction data to the controller 330 of the quantum computing system 330. The hardware controller module 330 of the controller 330 may then control the qubit manipulation hardware 340 to perform the correction to the one or more quantum devices 350 according to the correction data. Alternatively, the correction may be applied to a logical state measurement obtained from measurement of a logical state encoded in data qubits (in other words, the correction does not necessarily need to be applied to the physical qubits). Therefore in some cases, in addition to real-time state determination and syndrome / error identification, the readout apparatus 310 may perform real-time error correction.

[0062] Figure 7 illustrates an example method 400 according to the present disclosure which, for example, may be performed by a suitable apparatus or circuitry, for example the readout apparatus 310 of Figure 3. At step 410, one or more pertinent cells of a grid of cells are identified for an image frame. At step 420, one or more regions of interest in the image frame are identified, wherein each region of interest corresponds to a respective pertinent cell, and wherein each region of interest comprises one or more pixels of a plurality of pixels of the image frame. At step 430, image data for a row of pixels is received from an imaging device, wherein the image data is indicative of a number of photons received at each pixel. At step 440, the image data is converted into reduced image data, the reduced image data comprising image data only for pixels within the one or more regions of interest. Steps 430 and 440 may be repeated for additional rows of pixels. At step 450, based on the reduced image data, state information is determined for the one or more pertinent cells. State information may be determined for all pertinent cells after the reduced image data for the entire frame has been determined, or may be determined for a particular pertinent cell upon determining that all reduced image data for that cell has been determined.

[0063] Figure 8 illustrates the readout apparatus 310 according to the present disclosure. As can be seen from Figure 8, the readout apparatus includes one or more processor(s) 510 and one or more memories 520 coupled to one another (e.g. in a communication bus as shown in Figure 8 or in another arrangement). The processor(s) 510 and memory 520 may be configured to collectively perform the methods discussed herein, such as the method shown in Figure 7. In addition, the readout apparatus 310 may include communications interface 530, configured to receive data from and / or transmit data to one or more other devices, such as controller 530 and / or camera 520.

[0064] Furthermore, the methods described herein may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium (e.g. memory 520), containing instructions. Instructions embedded or encoded in a computer-readable medium may cause a programmable processor (e.g. processors 510), or other processor, to perform the method, e.g., when the instructions are executed. Computer-readable media may include non-transitory computer-readable storage media and transient communication media. Computer readable storage media, which is tangible and non-transitory, may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer-readable storage media. The term “computer-readable 12 storage media” refers to physical storage media, and not signals, carrier waves, or other transient media. As noted above, computer readable media may include transient communication media. Such communication media may occur within a single computer system or between multiple computer systems, and may take the form of transient signal-conveying media such as carrier waves and transmission signals.

[0065] Therefore, according to the present disclosure, methods, circuitry, systems, and computer-readable media are provided for reading data from a quantum computing system. Image data is received row-by-row of pixels, and the image data in converted to reduced image data row-by-row of pixels, as the image data is received. The reduced image data includes an indication of a number of photons received only at pixels included within predefined regions of interest, corresponding to particular cells of the quantum computing system. State information for the particular cells is determined based on the reduced image data, providing real-time data readout from the quantum computing system.

Claims

1. A computer-implemented method for reading data from a quantum computing system comprising a plurality of quantum devices arranged in a grid of cells, wherein the grid of cells comprises a plurality of rows of cells, wherein each cell of the grid of cells corresponds to a possible quantum device location, wherein each quantum device of the quantum computing system is configured to emit photons in response to a stimulus according to a state of the quantum device, and wherein the quantum computing system comprises an imaging device configured to capture a plurality of image frames of the grid of cells, the method comprising:for each of the plurality of image frames of the grid of cells:identifying one or more pertinent cells of the grid of cells for the image frame;identifying one or more regions of interest in the image frame, wherein each region of interest corresponds to a respective pertinent cell, and wherein each region of interest comprises one or more pixels of a plurality of pixels of the image frame;for a plurality of sets of pixels making up the image frame, wherein each of the sets of pixels comprises one or more rows of pixels:receiving, from the imaging device, image data for the set of pixels of the image frame, the set of pixels corresponding to a row of cells of the plurality of rows of cells, wherein the image data is indicative of a number of photons received at each pixel in the set of pixels,converting the image data into reduced image data, the reduced image data comprising image data only for pixels of the set of pixels within the one or more regions of interest, anddetermining, based on the reduced image data, state information for one or more pertinent cells in the row of cells.

2. The method according to claim 1, wherein converting the image data into reduced image data comprises discarding the image data for pixels of the set of pixels outside the one or more regions of interest.

3. The method according to any preceding claim, wherein the set of pixels corresponding to the row of cells comprises a plurality of rows of pixels, wherein receiving the image data comprises sequentially receiving image data for each of the plurality of rows of pixels, wherein converting the image data into reduced image data comprises, upon receiving the image data for a respective row of pixels, converting the image data for the respective row of pixels into reduced image data for the respective row of pixels, and wherein determining the state information for the one or more pertinent cells is based on the reduced image data for each of the rows of pixels of the set of pixels.

4. The method according to any preceding claim, wherein the state information for the one or more pertinent cells comprises information regarding an occupancy of the respective pertinent cell.

5. The method according to any preceding claim, wherein the state information for the one or more pertinent cells comprises information regarding a state of a quantum device within the respective pertinent cell.

6. The method according to claim 5, wherein the information regarding the state of a quantum device comprises an indication of the state of the quantum device and a certainty value for the state of the quantum device.

7. The method according to claim 6, wherein the information regarding the state of the quantum device is provided as a single value for each quantum device.

8. The method according to any preceding claim, wherein the one or more pertinent cells for a first image frame are different to the one or more pertinent cells for a second image frame.

9. The method according to any preceding claim, where identifying the one or more pertinent cells includes receiving, from a controller of the quantum computing system, an indication of the one or more pertinent cells for the image frame.

10. The method according to any preceding claim, wherein identifying the one or more pertinent cells comprises identifying respective co-ordinates in the grid of cells for the one or more pertinent cells.

11. The method according to any preceding claim, wherein identifying the one or more regions of interest in the image frame is based on a predetermined mapping between the grid of cells and co-ordinates of the pixels of the image frame.

12. The method according to any preceding claim, wherein the one or more pertinent cells include one or more cells comprising a syndrome quantum device.

13. The method according to any preceding claim, wherein each set of pixels comprises a plurality of rows of pixels, wherein the plurality of rows of pixels correspond to the row of cells.

14. The method according to any preceding claim, wherein the quantum computing system is a neutral-atom quantum computing system.

15. The method according to any preceding claim, wherein the quantum devices are qubits.

16. A computer-implemented method for identifying errors in a quantum computing system,the method comprising:the method according to any of claims 1-15; andwherein the method further comprises:identifying, based on the state information, syndrome data indicative of one or more errors in the state of one of more quantum devices in the grid of cells.

17. The method according to claim 16, wherein identifying the syndrome data is based on a comparison of the state information for two or more image frames.

18. The method according to claim 16 or claim 17, further comprising:determining, based on the syndrome data, a correction for an error state of one or more data quantum devices within the grid of cells.

19. Circuitry for reading data from a quantum computing system comprising a plurality of quantum devices arranged in a grid of cells, wherein the grid of cells comprises a plurality of rows of cells, wherein each cell of the grid of cells corresponds to a possible quantum device location, wherein each quantum device of the quantum computing system is configured to emit photons in response to a stimulus according to a state of the quantum device, and wherein the quantum computing system comprises an imaging device configured to capture a plurality of image frames of the grid of cells, wherein the circuitry is configured to execute the method according to any preceding claim.

20. A system comprising:the circuitry according to claim 19; andthe imaging device.

21. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1-19.17

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