Improvements in or relating to quantum computing

Abstract

There is provided a quantum computer comprising a module arranged in a plane, the module comprising a plurality of quantum processors, a radiation source configured to direct a beam of radiation towards the modules and a first reflector in the path of the beam of radiation and configured to redirect the beam of radiation to a direction substantially parallel to the plane of the modules.

Description

[0001] IMPROVEMENTS IN OR RELATING TO QUANTUM COMPUTING

[0002] The present invention relates to providing a scalable laser system for an ion trap quantum computer.

[0003] Quantum computing in general, unlike so-called “classical computing”, relies on the quantum mechanical properties of particles or matter to produce or alter data. The data may be represented by quantum bits or “qubits”, which is a two state quantum mechanical system. Unlike classical computing, the qubit may be in superposition of quantum states. Another feature of quantum computing is the entanglement between qubits in which the state of one particle or atom is influenced by another particle or atom.

[0004] Quantum mechanical qubits are able to encode information as combinations of zeros and ones simultaneously. Such properties open numerous complex numerical applications that are traditionally difficult for classical computers. Examples include artificial Intelligence, image processing and recognition, cryptography, or secure communications and so on.

[0005] Within an ion hyperfine electronic states (Zeeman split states) can be revealed by the use of a magnetic field and the different electron levels used as the different qubit states and electrons moved between the levels using microwave radiation or lasers.

[0006] In ion trap quantum computers (quantum charged coupled devices) ion traps can be used to control ions used in quantum computation and surface electrodes are used to generate electric fields to manipulate and trap the ions suspended in free space. The surface electrode potentials of an ion-trap are in turn controlled by DACs. State-of-the-art quantum computers use many DACs of the same type, for example 16 bit DACs with a better than 1 MHz update rate.

[0007] On a single chip there are a plurality of quantum gates. For example, on a chip of size 300x300mm there may be 4096 gate zones. However, there is a limit to the size of individual chips which can be easily manufactured. One solution is therefore to create an array of chips (or modules), as depicted in Figure 1 , with a few micrometers of spacing between each chip. Ions, or qubits, can be transferred between the different chips as necessary and therefore significantly larger computers can be developed. For example, a 10x10 array of chips, or modules, may have a 409,600 different gate zones.

[0008] Beams of radiation are used for a variety of purposes in quantum computers. They are used in the detection of the quantum state of the qubit and also to cool qubits. The beams are preferably highly coherent so that the diffraction is limited. Lasers are typically used and, for example, near UV lasers are often used in the detection of the quantum state. An example wavelength is 350nm.

[0009] Although highly coherent beams of radiation are often used there will still be some diversion and therefore the beam of radiation must be generated relatively close to the location of the ions. Significant divergence may mean that the beam of radiation is incident on other areas and therefore have undesirable effects such as electrically charging parts of the trap e.g. a dielectric oxide.

[0010] While quantum computers are, in terms of number of qubits, relatively small the provision of substantially non-divergent beams of radiation over the distances involved has been relatively simple as the distances involved are relatively small. However, as quantum computers increase in size it becomes more difficult to provide beams of radiation which remain sufficiently parallel.

[0011] A further issue is that the laser equipment may be relatively bulky and therefore occupy a large volume close to the position in which they are used and the space / volume occupied can limit the design of the quantum computers.

[0012] It is therefore an aim to provide an improved arrangement for the provision of beams of radiation.

[0013] According to the invention there is provided a method comprising providing a quantum computer comprising a module arranged in a plane, the module comprising a plurality of quantum processors each having a corresponding ion position where an operation can be performed on an ion, a radiation source configured to direct a beam of radiation substantially perpendicularly towards the plane of the module, a first reflector in the path of the beam of radiation and configured to redirect the beam of radiation along a radiation path substantially parallel to the plane of the module and a controller configured to control the quantum processors and the radiation source, wherein the method comprises irradiating, the beam of radiation, a plurality of ions, each in an ion position, along the radiation path.

[0014] The method may further comprise providing a plurality of ions at a plurality of the ion positions. This may be achieved by using ion traps, for example surface ion traps, to trap ions at ion positions.

[0015] The radiation source has a focal point but the plurality of ion positions are not at the focal point of the radiation source.

[0016] The radiation source may be a cooling laser and the controller may be configured to irradiate the plurality of ions for a period and at an intensity sufficient to cool the ions at any one of the ion positions along the radiation path. The ions may be irradiated for a longer period, or alternatively at a higher intensity compared to the irradiation and cooling of an ion arranged at the focal point of the radiation beam. The irradiation may be sufficient to cool an ion at any one of the ion positions below a predetermined temperature.

[0017] Each quantum processor may further comprise a detector and the controller is configured to set a detection threshold and / or a detection period of each detector such that at least two of the detectors have different detection thresholds and / or detection periods and wherein the detection thresholds and / or detection periods are based on the position in the beam of radiation. Thus, a detector further from the focal point has a lower detection threshold and / or a longer detection period than one closer to the focal point.

[0018] According to the invention there is provided a quantum computer comprising a module arranged in a plane, the module comprising a plurality of quantum processors each having a corresponding ion position where an operation can be performed on an ion, a radiation source configured to direct a beam of radiation substantially perpendicularly towards the plane of the module and a first reflector in the path of the beam of radiation and configured to redirect the beam of radiation along a radiation path substantially parallel (within 5°) to the plane of the module, wherein the radiation path intersects a plurality of the ion positions. In this way, the radiation source is taken out of the plane of the module and can be taken further away from the module, allowing more space. In particular the radiation source may be at least 5mm from the module. The radiation source may be more than 1cm from the module. The radiation beam should be sufficiently collimated as to not irradiate the surface material of the ion trap.

[0019] The quantum computer may further comprise a plurality of ions at a plurality of the ion positions.

[0020] The radiation source has a focal point along the radiation path parallel to the plane of the module and a plurality of ion positions are not at the focal point. In the present invention, the radiation beam is used to irradiate ions not at the focal point and the intensity or duration of the radiation beam, or the detectors can be adjusted such the all the ions complete the operation (e.g. cooling, detection, or a quantum gate operation). This allows a plurality of ions to be subjected to radiation simultaneously so the apparatus is more scaleable.

[0021] The quantum computer may further comprise a controller configured to control the radiation source to irradiate the plurality of ions for a period and at an intensity sufficient to cool the ions at any one of the ion positions along the radiation path.

[0022] A quantum computer may further comprise a controller and each quantum processor further comprise a detector and wherein the controller is configured to set a detection threshold and a detection period of each detector, at least two of the detectors having different detection thresholds and / or detection periods and wherein the detection thresholds and / or detection periods are based on the position in the beam of radiation. Thus, an ion position further from the focal position may have a longer detection period and / or a lower detection threshold than one closer to the focal point. The detection threshold and / or detection period is set so that the intensity of the radiation beam is compensated for and overall detection level is substantially the same across all of the ion positions. The radiation source is preferably configured to direct the beam of radiation towards the modules in a direction substantially perpendicular (85° -95°) to the plane of the module.

[0023] There may be a second reflector, arranged in the path of the radiation and configured to redirect the beam of radiation away from the module. The distance between the first and second reflectors is typically in the range of 30-300mm.

[0024] The device may also comprise an absorber configured to absorb the beam of radiation after reflection by the second reflector.

[0025] The module forms a qubit path along which a qubit may travel, the radiation path being substantially parallel to the plane of the modules and either intersecting or overlapping with the qubit path. A plurality of electrodes and signal generators may form a surface Paul trap. When operated, the plurality of electrodes form a qubit path along which the qubit may travel.

[0026] The one or more qubit path and the radiation path substantially parallel to the plane of the module preferably intersect and a diagonal angle of between 25° and 65°, and preferably 45°. The one or more qubit paths comprise gate zones in which gate operations are applied to a qubit and the radiation path intersects the qubit path at the gate zone. The gate zone has a magnetic field, in particular it may have a magnetic field gradient.

[0027] There may further be a plurality of radiation sources, a plurality of first reflectors in the path of a respective beam of radiation and a plurality of second reflectors in the path of the radiation.

[0028] There may be a first plurality of radiation sources which have radiation paths in a first direction parallel to the plane of the substrate and a second plurality of radiation sources which have radiation paths in a second direction parallel to the plane of the substrate and perpendicular to the first direction. The first plurality of radiation sources may have a wavelength in a first range and the second plurality of radiation sources have a wavelength in a second range. The first and second range may not overlap. The one or more qubit paths comprise gate zones in which a gate operation may be applied to a qubit and wherein the radiation path intersects the qubit path at the gate zone. As described above, the gate zones may have a magnetic field and / or a magnetic field gradient.

[0029] One or more of the reflectors may comprise a mirror. A particularly suitable mirror has been found to be Molybdenum coated with a dielectric material. The mirror surface may be aluminium with a protective dielectric coating to maximise reflectivity. An alternative reflector is a prism and a suitable prism may comprise sapphire, fused silica and / or quartz. Equally sapphire or glass can be used as mirror substrate and metallised with aluminium. These materials are particularly suitable as they have good compressive strength.

[0030] The reflector forms a support for the module. In this way the one or more modules may be supported and the reflector may form a structural portion of the apparatus. The reflector is preferably thermally stable with low coefficients of expansion.

[0031] There may be a plurality of modules, each module comprising a plurality of processors.

[0032] The one or more radiation sources may generate radiation at a wavelength in the range 250-1 OOOnm. As an example used in detection a wavelength range of 250-400nm, in particular 369nm may be used. One or more of the radiation sources may have a wavelength in the range 600-700nm in particular 635nm and be used in the cooling of qubits. One or more of the radiation sources may have a wavelength in the range 900-1 OOOnm, in particular 935nm and be used to repump qubits.

[0033] Figure 1 depicts a portion of a module;

[0034] Figure 2 depicts DC electrodes in a gate zone.

[0035] Figure 3 depicts a prior art arrangement; and

[0036] Figure 4 depicts a prior art arrangement;

[0037] Figure 5 depicts an arrangement according to the invention;

[0038] Figure 6 depicts an alternative arrangement according to the invention; Figure 7 depicts an arrangement according to the invention;.

[0039] Figure 8 depicts an arrangement of modules and prisms according to the invention;

[0040] Figure 9a depicts a prism according to the invention;

[0041] Figure 9b depicts a prism according to the invention;

[0042] Figure 10a depicts an arrangement according to the invention;

[0043] Figure 10b depicts and alternative arrangement according to the invention;

[0044] Figure 11 depicts an arrangement according to the invention; and

[0045] Figure 12 depicts an arrangement according to the invention.

[0046] A quantum processor comprises a plurality of electrodes to which voltages may be applied, by signal generators, to trap a qubit. One or more of the signal generators may generate a radio frequency signal which, when applied to a plurality of electrodes, can be used to confine an ion in two perpendicular directions. The ion is therefore suspended above a surface. This forms an energy trap known as a quadrupole ion trap or Paul trap. Other signal generators can then be used to generate signals which, when applied to a plurality of electrodes, form a potential well in a third direction, perpendicular to the other two directions, in which an ion can be trapped. The signals applied to different electrodes can be varied in order to move the position of the trapped ion. In this way the ion (forming a qubit) can be moved around above a module.

[0047] An example of part of a module is depicted in Figure 1 which depicts a surface linear Paul trap. The module comprises a plurality of electrodes to which voltages can be applied to form a potential well to trap an ion. Some electrodes 12 are RF electrodes, controlled by one or more signal generator 17 (for example an RF source), which generate an RF field. There may be a separate signal generators 17 for each electrode or alternatively one signal generator 17 may control several electrodes 12. Although coupled to the electrodes the signal generators may be remote. The RF field generated by these electrodes creates an ion trap in which the ion is positioned at a minimum energy and restricted by an energy barrier in the y and z direction. The generated RF field therefore restricts the ion in the y and z directions depicted in the figure. In a typical quantum processor the ion may be suspended above the electrodes, or module, at a height of 30-320um, in particular 125um. The RF field generated by the plurality of RF electrodes therefore creates a path of minimum energy in an x direction along which an ion can travel.

[0048] The RF electrodes 12 and associated signal generators 17 generate a radio frequency field with a time average energy depth. As an example, for RF DACs generating 200V amplitude at 20MHz at a height of 125um there would be a time average energy depth of 500meV for a Yb171 ion.

[0049] Additionally there are DC electrodes 11 , controlled by a DAC 16 configured to generate a DC field. The DACs 16 are coupled to the electrodes 11 and as depicted in figure 2 the DACs are often located remotely from the DC electrodes simply due to space constraints. There may be a different DAC for each electrode or a DAC may control a plurality of the electrodes. Different DC voltages can be applied to different electrodes to generate a potential well in which the ion is located. As the DC voltages of different electrodes are changed the ion is moved, along the path of minimum energy, in an x direction. Thus the combination of the RF electrodes 12 and the DC electrodes 11 control the position of the ion. The ion may therefore be moved around above the module as desired. Although DACs are used as an example, and type of signal generator can equally be used.

[0050] There will typically be hundreds or thousands of junctions and gate zones on a single module. However, in order to increase the capacity still further there may be a plurality of modules arranged adjacent to each other. Figure 2 depicts an example two dimensional arrangement of modules. Qubits, formed by trapped ions, may be held above a module but may also be passed across to another module.

[0051] A typical quantum processor requires different laser beams for variety of uses. Laser beams with a wavelength of 250-400nm, in particular 369nm are used to detect the state of a qubit so are used in detection. It is also important to keep qubits cool to reduce noise and lasers, of wavelength in the range 600-700nm, in particular 650nm are used in the cooling of qubits, particularly in the process of sympathetic cooling. Lasers are also sometimes used to repump the qubit and lasers having a wavelength in the range 900-1 OOOnm, in particular 935nm are used for this. Thus, a quantum computer will typically comprise one or more lasers and a prior art arrangement is depicted in figure 3 in which a laser 20 used to generate a laser beam above a module. The laser beam may be used in the detection of the state of a qubit and may have a wavelength of 250-400nm, in particular 369nm. Alternatively the laser may have a wavelength of in the range 600-700nm and be used for cooling qubits.

[0052] Although figure 3 depicts a single laser there may be a plurality of laser arranged around a module, some used for detection and some used for cooling. These may arranged in a grid fashion as depicted in figure 4 so that different laser beams address different qubit positions.

[0053] Although lasers are highly coherent there will naturally be some divergence so there may be a limited distance over which lasers can travel within a quantum computer before they either become ineffective or cause problems with other elements of the device due to the divergence of the laser.

[0054] Figure 5 depicts an arrangement according to the invention in which the laser 20 directs the laser beam towards, rather than parallel to, the plane of the module 10. The laser beam is preferably directed substantially perpendicularly towards the plane of the module. A prism 25 is arranged in the path of the laser beam which reflects the beam to a direction parallel to the plane of the module. In this way the laser beam travels along a path above the module and parallel to the plane of the module and can interact with any qubits suspended above the module in the path of the laser beam. The laser and the prism are configured to direct the laser beam on a parallel path, the height of which above the module is the same height as the height of the minimum energy of the ion trap. As an example height, the laser beam may be directed at a height of 100-150um above the module, in particular 125um. Laser beams directed in this way can be used to cool qubits suspended above the module 10 in a quadrupole ion trap. Alternatively laser beams directed in this way can be used in the detection of qubits suspended above the module.

[0055] The laser beam may have a width of 100um or more, such that it can interact with a qubit. The width of the laser beam and the divergence are inversely related so an decrease in the width would result in an increase in divergence. The prism should be grounded to prevent any excess charge build up. Furthermore, the prism can form part of a support for the modules themselves.

[0056] The prism is preferably made of a thermally stable material with limited expansion. Sapphires have been found to be particularly suitable as reflective prisms for this purpose.

[0057] As an alternative to a prism a mirror can be used and again, a thermally stable material is preferable. An example mirror is Molybdenum coated with a dielectric, for example aluminium.

[0058] Figure 6 depicts a further example of the invention in which there are a plurality of prisms 25. A second side of the prism can be used to reflect the laser beam back towards an absorber 30 in which the laser is absorbed. Thus, the path of the laser is limited such that only limited divergence occurs within the path. Furthermore, the laser beam is directed away from the module after the parallel path is complete and this reduces any excess heat. The distance between adjacent prisms may be in the range 30-300mm.

[0059] Figure 6 depicts different sides of the prism being used to reflect the laser beam onto, and out of the parallel path. As will be appreciated by the skilled person, different prisms can equally well be used.

[0060] Figure 7 depicts a plan of an individual module 10 with associated prisms, laser and absorbers. The prisms 25 are elongate and form trusses along which the module is supported. There are a plurality of radiation sources 20 along the left hand side, each of which projects a laser beam towards the prism, where the laser beam is redirects along a parallel path towards a corresponding prism the opposite side of the module. The corresponding prism redirects the laser beam upwards towards the corresponding absorber 30. On the top side there are more radiation sources 20 which direct laser beams towards a prism where the lasers are redirected along a parallel path towards a prism on the other side. In this way a grid of laser beams may be developed individual qubits can be addressed. In one example, the lasers along the left hand side may be lasers used in detection with a wavelength of, for example, 369nm and lasers along the top side may be lasers used in cooling and to repump the qubit. The radiation sources may be lasers or alternatively the lasers may be located elsewhere and radiation transmitted through fibre optic cables closer to the module. Beam collimation and preparation optics then form the radiation into individual beams. Furthermore, a laser beam may be split into several different beams by a splitter, and then used as several radiation sources.

[0061] Figure 8 depicts a larger grid arrangement comprising a plurality of modules 10 and prisms 25. For simplicity, the lasers and absorbers have not been depicted although each module may have associated lasers and absorbers as depicted in Figure 7.

[0062] When multiple modules 10 are used within a single quantum computer qubits may pass from one module to another. To allow this the prism 10 (or reflector) may have a passage, or aperture, therethrough and Figures 9a and 9b depicts such a prism. Figure 9a depicts a prism 10 in which there are a plurality of holes 26 therethrough, through which the ion may pass to a neighbouring module. The height of the holes is the height at which ions (qubits) are suspended above the module. Figure 9b depicts an alternative arrangement in which there are a plurality of arches 27.

[0063] Figure 10a depicts an arrangement of radiation paths and qubit paths. As can be seen, the qubit paths 30 and the radiation paths intersect each other diagonally and intersect each other at an angle of 45°. The qubit paths have different areas and the areas in which gate operations occur is known as a gate zone. In the gate zone there is a magnetic field, which may be a magnetic gradient. The radiation path and the qubit paths preferably intersect at the gate zone so that cooling and detection can occur at the gate zone. Figure 10a depicts an arrangement in which there are radiation sources along a first side of the module and figure 10b depicts and arrangement in which there are radiation sources along first and second sides of the module. The radiation sources along a first side of the module may be radiation sources used in the detection of qubits i.e. having a wavelength suitable for detection. The radiation sources along a second side may be radiation sources used in the cooling and / or repumping of qubits. Although figures 10a and 10b depict the radiation paths and the qubit paths overlapping at 45 they could also intersect diagonally at another angle. Other suitable angles of intersection may be 30° and 60°.

[0064] Figure 11 depicts an arrangement in which a plurality of ions are arranged in the beam of radiation. The radiation beam has a focal point, FP, and there are a plurality of ion positions, 111 , 112, 113, 114. An ion position is a position at which an ion may be position and an operation may be performed on the ion. As an example, the beam of radiation may perform a cooling operation or a detection operation or a quantum gate operation on ions positioned at the ion positions.

[0065] In the example depicted in Figure 11 , none of the ion positions are at the focal point of the beam of radiation. However, in some examples one of the ion positions may be located at the focal point.

[0066] Also depicted in Figure 11 is a controller 115 which controls the laser 20. In this example, the laser 20 is used for cooling the ions. The laser may have a wavelength of, for example 369nm but the exact wavelength will depend upon the type of ion being cooled. There are ions positioned at the ion positions and the laser irradiates the ions. Ions positioned at positions 112 and 113 are closer to the focal point of the radiation beam and therefore the laser is more concentrated at those ion positions and therefore the ions will be cooled faster. In order for the ions further from the focal point to be cooled below a threshold the laser must be operated at a higher intensity and / or for longer. However, the controller controls the laser to operate for a period sufficient to cool ions to below a predetermined termperature at at least ion positions at which ions are located. For example, if ions are located at ion positions 111 and 113 the controller controls the laser to operate for a duration and / or at an intensity sufficient to cool ions at both locations to below a predetermined threshold. The laser may be operated for longer, or alternatively (and additionally) at a higher intensity in order to cool ions not positioned at the focal point. The laser may cool each ion to below 100mK, or to below 10mK. An alternative form of cooling, sideband cooling may cool each ion to below 1 quanta.

[0067] The controller may control the laser to operate for a period / at an intensity sufficient to cool ions at any one of the ion positions in the radiation path to below the predetermined threshold. Alternatively, the controller may know which ion positions are occupied and control the laser to operate for a period / at an intensity sufficient to cool ions at only the occupied ion positions to below the predetermined threshold.

[0068] Figure 12 depicts an arrangement in which the laser 20 emits a beam of radiation used for detection. A laser beam for detection may also be 369nm, but again it will depend on the type of ion. At each of the positions there is a detector 121 , 122, 123, 124. Each detector detects photons emitted at the respective ion position. As the ion positions 112 and 113 are closer to the focal point FP, more photons will be emitted than for ions at ion positions 111 and 114. Therefore, the detection threshold for detectors 112 and 113 is set, by a controller, higher than the detection thresholds for detectors 111 and 114. Alternatively, or additionally, the detection period for detectors closer to the focal point may be shorter than the detection period for the detectors further from the focal point. The detection period and the detection threshold are set by a controller. In this way the overall sensitivity is substantially the same across all the ion positions despite the different laser intensity at the different positions. Thus, a single beam of radiation can be used for detection on a plurality of ions.

[0069] An alternative to the qubit paths and the radiation paths intersecting diagonally is for the radiation paths and the qubits to substantially overlap but to have a dog leg path for the qubit near to the reflector to direct the qubit through a passage.

[0070] Although the term “prism” has been used throughout the description it will be understood that any reflector can equally be used.

[0071] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0072] “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0073] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments. It is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1 . A method comprising providing a quantum computer comprising: a module arranged in a plane, the module comprising a plurality of quantum processors each having a corresponding ion position where an operation can be performed on an ion; a radiation source configured to direct a beam of radiation substantially perpendicularly towards the plane of the module; a first reflector in the path of the beam of radiation and configured to redirect the beam of radiation along a radiation path substantially parallel to the plane of the module; and a controller configured to control the quantum processors and the radiation source, wherein the method comprises irradiating, the beam of radiation, a plurality of ions, each in an ion position, along the radiation path.

2. A method according to claim 1 wherein the radiation source has a focal point and wherein a plurality of the ion positions are not at the focal point of the radiation source.

3. A method according to either claim 1 or claim 2 wherein the radiation source is a cooling laser and wherein the controller is configured to irradiate the plurality of ions for a period and at an intensity sufficient to cool the ions at any one of the ion positions along the radiation path.

4. A method according to claim 3 wherein the irradiation is sufficient to cool an ion at any one of the plurality of ion positions below a predetermined temperature.

5. A method according to any one of the preceding claims wherein each quantum processor further comprises a detector and the controller is configured to set a detection threshold and / or a detection period for each detector wherein at least two of the detectors have different detectionthresholds and / or detection periods and wherein the detection thresholds and / or detection periods are based on the position in the beam of radiation.

6. A quantum computer comprising: a module arranged in a plane, the module comprising a plurality of quantum processors each having a corresponding ion position where an operation can be performed on an ion; a radiation source configured to direct a beam of radiation substantially perpendicularly towards the plane of the module; a first reflector in the path of the beam of radiation and configured to redirect the beam of radiation along a radiation path substantially parallel to the plane of the module, wherein the radiation path intersects a plurality of the ion positions.

7. A quantum computer according to claim 6 wherein the radiation source has a focal point and wherein a plurality of the ion positions are not at the focal point.

8. A quantum computer according to either claim 6 or claim 7 further comprising a controller configured to control the radiation source to irradiate the plurality of ions for a period and at an intensity sufficient to cool the ions at any one of the ion positions along the radiation path.

9. A quantum computer according to any one of claims 6 to 8 and further comprising a controller and each quantum processor further comprising a detector and wherein the controller is configured to set a detection threshold and / or a detection period for each detector, at least two of the detectors having different detection thresholds and / or detection periods and wherein the detection thresholds and / or detection periods are based on the position in the beam of radiation.

10. A quantum computer according to any one of claims 6 to 9 and further comprising a second reflector, arranged in the path of the radiation and configured to redirect the beam of radiation away from the module.

11. A quantum computer according to claim 10 further comprising an absorber configured to absorb the beam of radiation after reflection by the second reflector.

12. A quantum computer according to any one of claims 6 to 11 , the module forming a qubit path along which a qubit may travel, and whereinthe radiation path being substantially parallel to the plane of the module either intersecting or overlapping with the qubit path.

13. A quantum computer according to claim 12 wherein the one or more qubit path and the radiation path substantially parallel to the plane of the module intersect at a diagonal angle of between 25° and 65°.

14. A quantum computer according to either claim 12 or claim 13 wherein the one or more qubit paths comprise gate zones in which a gate operation may be applied to a qubit and wherein the radiation path intersects the qubit path at the gate zone.

15. A quantum computer according to any one of claims 6 to 14 wherein the first reflector comprises a passage through which a qubit can pass.

16. A quantum computer according to any one of claims 6 to 15further comprising a plurality of radiation sources, a plurality of first reflectors in the path of a respective beam of radiation and a plurality of second reflectors in the path of the radiation.

17. A quantum computer according to claim 16 wherein a first plurality of radiation sources have radiation paths in a first direction parallel to the plane of the substrate and a second plurality of radiation sources have radiation paths in a second direction parallel to the plane of the module and perpendicular to the first direction.

18. A quantum computer according to claim 17 wherein the first plurality of radiation sources have a wavelength in a first range and the second plurality of radiation sources have a wavelength in a second range.

19. A quantum computer according to any one of claims 6 to 18 wherein at least one of the first and second reflector comprises a mirror.

20. A quantum computer according to any one of claims 6 to 19 wherein at least one of the first and second reflector comprises a prism.21 . A quantum computer according to any one of claims 6 to 20 wherein the reflector forms a support for the module.

22. A quantum computer according to any one of claims 6 to 21 further comprising a plurality of modules, each module comprising a plurality of processors.

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