Optical arrangement for a quantum computer, quantum computing arrangement and quantum computer

Abstract

According to an embodiment, the optical arrangement (10) for a quantum computer comprises a first (1), a second (2) and a third (3) mirror for focusing radiation from a laser (4) onto an ion crystal (6) of several ions (6'), wherein the ions are lined up along a predefined line (7). The first and the second mirror are configured to transform, via reflection at the first and the second mirror, a beam from the laser having a circular beam profile into a beam with an elongated beam profile. The third mirror is configured to focus the beam with the elongated beam profile coming from the second mirror onto the ion crystal such that the elongated beam profile is maintained and such that, at the location of the ion crystal, the elongated beam profile is aligned with the predefined line.

Description

[0001] Description

[0002] Optical arrangement for a quantum computer, quantum computing arrangement and quantum computer

[0003] The present disclosure relates to an optical arrangement for a quantum computer, to a quantum computing arrangement and to a quantum computer .

[0004] One obj ect to be achieved is to provide an optical arrangement which contributes to a reliable cooling and / or read-out of qubits . Further obj ects to be achieved are to provide a quantum computing arrangement with such an optical arrangement and a quantum computer with such an optical arrangement .

[0005] First , the optical arrangement is speci fied .

[0006] According to an embodiment , the optical arrangement for a quantum computer comprises a first , a second and a third mirror for focusing radiation from a laser onto an ion crystal of several ions , wherein the ions are lined up along a predefined line . The first and the second mirror are configured to trans form, via reflection at the first and the second mirror, a beam from the laser having a circular beam profile into a beam with an elongated beam profile . The third mirror is configured to focus the beam with the elongated beam profile coming from the second mirror onto the ion crystal such that the elongated beam profile is maintained and such that , at the location of the ions , the elongated beam profile is aligned with the predefined line . In other words , the optical arrangement comprises an optical system comprising a first and a second mirror . This optical system reali zes a reflective telescope and is configured to take a laser beam, which typically has a circular profile , and convert it into an elongated / elliptical beam profile . The beam is collimated after passing through the telescope , with a long axis and a short axis , respectively . The long axis of the collimated beam may then be perpendicular to the axis of the ion crystal , and the short axis parallel to it . A third mirror, which may be a concave or an of f-axis parabolic mirror, is used to focus the collimated elliptical beam onto the ion crystal . Thereby, due to the reflection, the beam profile may be rotated such that the long axis is parallel to the ion crystal when the beam hits the ion crystal .

[0007] A large-scale ion trap-based quantum computer necessitates a substantial string of ions positioned within a uni form optical field comprising various wavelengths . To ensure the common focus at the ions ' positions despite the di f ferent wavelengths involved, chromatic aberration should be minimi zed . Both problems are solved by the speci fied optical arrangement , which can also be called "reflective telescope" . Indeed, the mirrors of the optical arrangement enable the beam spot from a laser to be made elongated or elliptical , respectively . On the other hand, the usage of mirrors instead of lenses reduces chromatic aberration .

[0008] The beam profile of a laser beam is the profile of the crosssection of the beam when cut perpendicularly to the propagation direction .

[0009] During operation, the laser beam may first hit the first mirror . After reflection at the first mirror, it hits the second mirror, is reflected therefrom and then hits the third mirror . By way of example , the first mirror is configured to trans form, via reflection, the beam from the laser having a circular beam profile into a beam with an elongated beam profile . The second mirror may then be configured to reflect the beam with the elongated beam profile from the first mirror onto the third mirror, whereby the elongated shape of the beam profile is maintained or even strengthened .

[0010] The optical arrangement may be arranged such that laser radiation reflected from the first mirror trans fers to the second mirror without passing any other optical element . Likewise , the optical arrangement may be arranged such that laser radiation reflected from the second mirror can trans fer to the third mirror without passing any other optical element . In other words , the space between the first mirror and the second mirror and / or the space between the second mirror and the third mirror is empty, i . e . only filled with gas or vacuum .

[0011] The third mirror is configured to focus the laser radiation with the elongated beam profile onto the ion crystal such that the elongated beam profile and the ion crystal are aligned at the location of the ions crystal . This means that the length axis of the elongated beam profile and the predefined line are orientated in the same direction at the location of the ion crystal . For example , the length axis and the predefined line are parallel to each other or include an acute angle of , for example , at most 10 ° . "At the location of the ion crystal" means that , when beam profile is proj ected onto a plane through the ion crystal and parallel to the predefined line , the beam spot on this plane is elongated with the length axis being parallel to the predefined line . The focusing by the third mirror may result in a rotation of the length axis by 90 ° . Thus , when hitting the third mirror, the length axis of the elongated beam profile may be perpendicular to the predefined line .

[0012] According to a further embodiment , the first and / or the second and / or the third mirror are concave mirrors . That is , the reflective surfaces of the first and / or the second and / or the third mirror have a concave shape .

[0013] According to a further embodiment , the first and / or the second mirror are aspheric mirrors . The third mirror may be aspheric or spheric . A spheric mirror is a mirror with a constant local curvature of the reflective surface over the whole surface . An aspheric mirror is a mirror with a nonconstant local curvature of the reflective surface .

[0014] According to a further embodiment , the first and / or the second mirror are asymmetric mirrors . In this context , "asymmetric" means that the reflective surface of the mirror is not circularly symmetric with respect to a rotation around the optical axis . It may however have a n- fold rotational symmetry for a rotation around the optical axis .

[0015] Asymmetric mirrors are characteri zed in that the curvature of the reflective surface depends on the direction along the reflective surface . Particularly, an asymmetric mirror may have at least two di f ferent focal lengths . For example , rays are focused with a first focal length in the direction of a first axis and are less focused ( e . g . with a second focal length) in the direction of a second axis . The first axis and the second axis may be orthogonal to each other . Both axes are perpendicular to the optical axis of the respective mirror and may intersect with the optical axis at a common point .

[0016] The first focal length may be a minimum focal length of the respective mirror . The second focal length may be a maximum focal length of the respective mirror . For example , the second focal length is infinite . That is , the curvature of the reflective surface when moving along the reflective surface and parallel to the second axis is zero or the curvature radius is infinite , respectively . The asymmetric mirror or the reflective surface thereof may be formed mirror-symmetric with respect to the first and / or the second axis .

[0017] According to a further embodiment , the second axes of the first and the second mirror are parallel to each other . In this way, the elongated shape of the beam profile can be maintained or even be increased when the laser beam is reflected at the second mirror . The second axes may be perpendicular to the predefined line .

[0018] According to a further embodiment , at least one of the first and the second mirror is a cylindrical mirror . A cylindrical mirror is an asymmetric mirror with the curvature of the reflective surface along one axis , namely the second axis , being zero . Particularly, the reflective surface has the shape of a section of a cylindrical shell . For example , the first and the second mirrors are cylindrical mirrors . The first focal length is , for example , below 1 m .

[0019] In other words : A cylindrical mirror is a type of curved mirror with a reflective surface that is shaped like a section of a cylinder. Unlike spherical mirrors, which have a portion of a sphere as their reflective surface, cylindrical mirrors have a section of a cylinder's curved surface. A cylindrical mirror has two different radii of curvature in two directions. The reflective surface of a cylindrical mirror is curved in one direction (either convex or concave) , creating one principal curvature, while the curvature in the perpendicular direction remains flat or essentially infinite in radius .

[0020] According to a further embodiment, the third mirror is an aspheric mirror, e.g. an asymmetric mirror. The third mirror may be a cylindrical mirror or a mirror with the minimum and maximum focal length being finite. For example, the minimum and maximum focal length are both below 1 m.

[0021] According to a further embodiment, the third mirror is a symmetric mirror. A symmetric mirror is characterized by a circular symmetry of the reflective surface for a rotation around the optical axis. For example, the third mirror is a parabolic mirror. Alternatively, the third mirror may be a spherical mirror.

[0022] According to a further embodiment, a focal point of the first mirror lies in the region between the first and the second mirror. For example, the focal point associated with the first focal length of the first mirror lies in the region between the first and the second mirror.

[0023] According to a further embodiment, the distance between the first and the second mirror is equal to the sum of a focal length LI of the first mirror and a focal length L2 of the second mirror. The focal length LI of the first mirror is, for example , the first focal length of the first mirror . Likewise , the focal length L2 of the second mirror may be the first focal length of the second mirror . With this arrangement , parallel laser rays which incident on the first mirror are focused, are then incident on the second mirror and are reflected therefrom so that they are again parallel .

[0024] According to a further embodiment , the first and / or the second and / or the third mirror are of f-axis mirrors . For example , the third mirror is an of f-axis parabolic mirror . Of f-axis mirrors spatially separate the focal point from the rest of the beam path .

[0025] Next , the quantum computing arrangement is speci fied .

[0026] According to an embodiment , the quantum computing arrangement comprises an ion trap which is configured to trap an ion crystal of several ions lined up along a predefined line . The quantum computing arrangement further comprises an optical arrangement according to any of the embodiments described herein . The ion trap and the optical arrangement are arranged such that the trapped ion crystal is located in a focal point of the third mirror .

[0027] Since the quantum computing arrangement comprises the optical arrangement speci fied herein, all features disclosed for the optical arrangement are also disclosed for the quantum computing arrangement and vice versa .

[0028] During operation of the ion trap, ions are trapped inside the ion trap along a predefined line . The ion trap is , for example , configured to trap at least one ion crystal with two or more ions , e . g . at least eight or at least 20 or at least 100 and / or at most 1000 ions lined up along the predefined line . The predefined line may be a straight line . The fact that the ions are trapped along the predefined line means , in particular, that each of the trapped ions intersects with the predefined line and / or oscillates around the predefined line .

[0029] The ion trap may comprise electrodes for establishing an electric trapping potential in which the ions are trapped along the predefined line . The ion trap may be a so-called quadrupole trap . Particularly, the ion trap is a Paul trap . For example , the ion trap is a planar Paul trap . The electrodes may comprise at least two DC electrodes and at least two or at least four AC electrodes . The electrodes may be arranged on the top side of a substrate or on the bottom side of the substrate or may be arranged in the substrate . For example , the ion trap is a planar ion trap with the electrodes being metalli zations at the top side of the substrate .

[0030] When the ion trap is in operation, the ion crystal is arranged in a focal point of the third mirror . Particularly, the ion crystal intersects with the focal point . The focal point may be associated with the minimum focal length or first focal length, respectively, of the third mirror .

[0031] According to a further embodiment , the predefined line is orthogonal to the second axes of the first and the second mirror . The third mirror then focusses the beam onto the ion crystal and the length axis of the beam profile is parallel to the predefined line .

[0032] According to a further embodiment , the quantum computing arrangement comprises a laser which is arranged such that the beam of the laser is impinged onto the first mirror . Particularly, the beam is impinged such that the beam profile of the laser is deformed in an elongated manner by the reflection . For example , the beam profile from the laser is circular-shaped and becomes elongated, particularly elliptical , by the reflection at the first mirror .

[0033] According to a further embodiment , the laser, the optical arrangement and the ion trap are arranged such that , during operation, the predefined line is aligned to , e . g . parallel to , the length axis of the elongated beam profile at the location of the ion crystal . In this way, ions can be illuminated uni formly with laser radiation .

[0034] According to a further embodiment , the radiation of the laser covers a wavelength range of at least 100 nm or at least 200 nm or at least 500 nm . For example , the full width at hal f maximum ( FWHF) of the laser radiation is at least 100 nm or at least 200 nm or at least 500 nm . The wavelength range , particularly the FWHM, may be at most 3 pm or at most 2 pm .

[0035] According to a further embodiment , the quantum computing arrangement comprises a vacuum chamber . During operation, the ions are trapped in the vacuum chamber . The ion trap and, optionally, the optical arrangement may be arranged in the vacuum chamber . Alternatively, the optical arrangement is arranged outside the vacuum chamber . The vacuum chamber may be an ultra-high vacuum chamber, an extreme-high vacuum chamber and / or a cryostat .

[0036] Next , the quantum computer is speci fied . The quantum computer comprises a quantum computing arrangement as described herein . Therefore , all features disclosed for the quantum computing arrangement are also disclosed for the quantum computer and vice versa .

[0037] The quantum computer is configured to perform quantum computations by using the quantum computing arrangement . The trapped ions of the quantum computing arrangement can be cooled and / or read-out by using the optical arrangement .

[0038] The laser and / or the optical arrangement may be part of a laser-based cooling and / or read-out system of the quantum computer . The cooling system is configured for cooling the ions in order to prepare them in low motional states and trap them in their respective ground states . The read-out system is configured for determining the state of each ion . For example , the ions are cooled and / or read-out by impinging the laser beam of the laser on them .

[0039] Hereinafter, the optical arrangement , the quantum computer arrangement and the quantum computer will be explained in more detail with reference to the drawings on the basis of exemplary embodiments . The accompanying figures are included to provide a further understanding . In the figures , elements of the same structure and / or functionality may be referenced by the same reference signs . It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale . Insofar as elements or components correspond to one another in terms of their function in di f ferent figures , the description thereof is not repeated for each of the following figures . For the sake of clarity, elements might not appear with corresponding reference symbols in all figures . Figures 1 to 3 show an exemplary embodiment of the quantum computing arrangement and the optical arrangement in di f ferent views ,

[0040] Figure 4 shows a further exemplary embodiment of the quantum computing arrangement , and

[0041] Figure 5 shows an exemplary embodiment of the quantum computer .

[0042] Figure 1 shows an exemplary embodiment of the quantum computing arrangement 100 when viewed antiparallel to a z- direction . The x-direction points from the left to the right and the y-direction points upwards . The quantum computing arrangement 100 comprises an exemplary embodiment of the optical arrangement 10 which comprises a first mirror 1 , a second mirror 2 and a third mirror 3 . The three mirrors 1 , 2 , 3 are arranged such that a laser beam is reflected in a zigzag path . Parallel rays from a laser are reflected at the first mirror 1 , are focused in a focal point Fl of the first mirror 1 , then hit the second mirror 2 from which the rays are reflected such that they are again parallel to each other . Afterwards , the rays hit the third mirror 3 and are reflected from the third mirror 3 such that they are focused onto an ion crystal 6 .

[0043] The first 1 and the second 2 mirror are aspheric and asymmetric mirrors , e . g . cylindrical mirrors . The optical axes of both mirrors are parallel to the x-direction . Both mirrors 1 , 2 are focusing in the y-direction ( first axis ) and are less focusing or not focusing in the z-direction ( second axis ) . The sum of the focal length LI , L2 associated with the first axes is equal to the distance D between the mirrors 1,

[0044] 2.

[0045] The quantum computing arrangement 100 further comprises an ion trap 20 (indicated by the dashed lines) in the form of a planar Paul trap. The ion trap 20 comprises a substrate 22, e.g. of sapphire or silicon, and a plurality of electrodes 21 on top of the substrate 22. The electrodes 21 are configured to realize an electric trapping potential. During operations, ions 6' are trapped in the electric trapping potential along a predefined line 7. The predefined line 7 is parallel to the y-direction. Particularly, the trapped ions 6' , which form the ion crystal 6, are arranged in a focal point of the third mirror 3. The third mirror 3 is, for example, an aspheric mirror. By way of example, it is an off-axis parabolic mirror .

[0046] Figure 2 shows the quantum computing arrangement 100 of figure 1 in a different view, namely in a cross-sectional view with the cut-plane through the ion crystal 6 and parallel to the z- and y-direction. That is, the viewing direction is antiparallel to the x-direction. The first mirror 1 and the third mirror 3 are visible. The beam profile of the laser beam as incident on the first mirror 1 is indicated by the dashed circle. Thus, the beam profile is circular-shaped. However, due to the characteristics of the first mirror 1 and the second mirror 2, the beam profile is stretched when reflected from the first mirror 1 and the second mirror 2 so that a beam profile with an elliptical shape as indicated by the vertically orientated ellipse hits the third mirror 3. The third mirror 3 focuses in the z- direction so that the ions 6' of the ion crystal 6 are uniformly illuminated as indicated by the horizontally ellipse . The length axis of the ellipse is parallel to the predefined line 7 .

[0047] Figure 3 shows the quantum computing arrangement 100 of figures 1 and 2 in a cross-sectional view with the cut-plane through the ion crystal 6 and parallel to the z- and y- direction . Now, the viewing direction is parallel to the x- direction . It can be seen that an elliptical shaped beam profile ( see dashed ellipse ) hits the second mirror 2 . When this beam is reflected at the second mirror 2 , the elliptical shape is maintained or the elliptical shape is even further elongated .

[0048] Figure 4 shows a further exemplary embodiment of the quantum computing arrangement 100 . The quantum computing arrangement 100 further comprises a laser 4 which generates the laser beam with the substantially circular beam profile which hits on the first mirror 1 . The quantum computing arrangement 100 further comprises a vacuum chamber 30 . The optical arrangement 10 and the ion trap 20 are arranged in the vacuum chamber 30 .

[0049] An exemplary embodiment of a quantum computer 1000 is shown in figure 5 . The quantum computer 1000 comprises a quantum computing arrangement 100 according to one of the exemplary embodiments described herein . The ion trap 20 and the laser 4 are connected to external components of the quantum computer 1000 partially through the chamber 30 by a plurality of connections 110 . For instance , the connections 110 connect the ion trap 20 with external control electronics 120 and a classical computer 130 . The quantum computing arrangement 100 is configured to trap, manipulate and measure trapped ions . For this purpose , the quantum computing arrangement 100 may comprise , besides the laser 4 , the optical arrangement 10 and the ion trap 20 , light guides and / or internal electronics comprising electronic devices . The electronic devices can comprise circuitry, integrated electronics , power supply and / or detectors , such as photon detectors and / or charge detectors , controllers etc . Exemplarily, the internal electronics are provided for pre-processing . For example , these components allow a measurement of a respective state of the ion and allow gate operations on the ion . Thus , the quantum computing arrangement 100 is configured to trap the ions as well as to carry out operations and measurements on the trapped ions .

[0050] The ion trap 20 and the optical arrangement 10 are mounted in a chamber 30 , wherein the chamber 30 can be an ultra-high vacuum chamber, an extreme-high vacuum chamber and / or a cryostat .

[0051] The quantum computing arrangement 100 , particularly the ion trap 20 and the laser 4 , is connected to the external electronics 120 via the connections 110 . The external electronics 120 can be located at least partially inside and partially outside the chamber 30 . Further, the external electronics 120 is connected to the classical computer 130 .

[0052] The external electronics 120 comprises , for instance , analog to digital converters as well as signal generators such as radio frequency generators , microwave signal generators , low- frequency signal generators and / or direct current signal generators . Furthermore , the external electronics 120 can comprise a transistor-transistor logic, TTL . The classical computer 130 is configured, for example , to provide and receive digital signals . The digital signals correspond to control signals used for operations on the qubits / ions as well as to measurement signals corresponding to a state of the qubits .

[0053] The external electronics 120 is , inter alia, configured to convert the digital signals to analog signals and vice versa . Therefore , the external electronics 120 is configured to provide the converted analog signals for manipulating the ions ( qubits ) to the quantum computing arrangement 100 . Further, the external electronics 120 is configured to provide measured analog signals from the quantum computing arrangement 100 to the classical computer 130 or to process such signals to directly initiate some response signal generated by the control electronics 120 .

[0054] The classical computer 130 is exemplarily configured to be provided with a speci fic algorithm, i . e . a predetermined quantum calculation solving a speci fic problem . The classical computer 130 is then configured to convert a compiled code corresponding to the algorithm to commands for the quantum computing arrangement 100 . The commands are subsequently forwarded via the external control electronics 120 to the quantum computing arrangement 100 . Furthermore , the classical computer 130 is configured to receive a measured outcome of the speci fic algorithm .

[0055] For example , all elements of the quantum computer 1000 , in particular all electronic elements of the quantum computer 1000 , are synchroni zed by an atomic clock reference , for example . The invention is not limited to the exemplary embodiments by their description . Rather, the invention encompasses any new feature as well as any combination of features , which in particular includes any combination of features in the claims , even i f this feature or combination itsel f is not explicitly indicated in the claims or exemplary embodiments .

[0056] Reference sign list :

[0057] 1 first mirror

[0058] 2 second mirror

[0059] 3 third mirror

[0060] 4 laser

[0061] 6 ion crystal

[0062] 6 ' ion

[0063] 7 predefined line

[0064] 10 optical arrangement

[0065] 20 ion trap

[0066] 21 electrode

[0067] 22 substrate

[0068] 30 vacuum chamber

[0069] 100 quantum computing arrangement

[0070] 110 connections

[0071] 120 external electronics

[0072] 130 classical computer

[0073] 1000 quantum computer

[0074] LI focal length

[0075] L2 focal length

[0076] Fl focal point

[0077] D distance

Claims

Claims1. Optical arrangement (10) for a quantum computer, comprising- a first (1) , a second (2) and a third (3) mirror for focusing radiation from a laser (4) onto an ion crystal (6) of several ions (6' ) lined up along a predefined line (7) , wherein- the first (1) and the second (2) mirror are configured to transform, via reflection at the first (1) and the second (2) mirror, a beam from the laser (4) having a circular beam profile into a beam with an elongated beam profile,- the third mirror (3) is configured to focus the beam with the elongated beam profile coming from the second mirror (2) onto the ion crystal (7) such that the elongated beam profile is maintained and such that, at the location of the ion crystal (6) , the elongated beam profile is aligned with the predefined line (7) .

2. Optical arrangement (10) according to claim 1, wherein- the first (1) and the second (2) mirror are aspheric mirrors .

3. Optical arrangement (10) according to claim 2, wherein- the first mirror (1) and the second mirror (2) are each characterized by two orthogonal axes, namely a first axis and a second axis, which are both perpendicular to the optical axis of the respective mirror (1, 2) , wherein each mirror (1, 2) focuses in the direction of the first axis and focuses less in the direction of the second axis,- the second axes of the first (1) and the second (2) mirror are parallel to each other.

4. Optical arrangement (10) according to any one of the preceding claims, wherein- at least one of the first (1) and the second (2) mirror is a cylindrical mirror.

5. Optical arrangement (10) according to any one of the preceding claims, wherein- the third mirror (3) is an aspheric mirror.

6. Optical arrangement (10) according to claim 5, wherein- the third mirror (3) is a parabolic mirror.

7. Optical arrangement (10) according to any one of the preceding claims, wherein- a focal point (Fl) of the first mirror (1) lies in a region between the first (1) and the second mirror (2) .

8. Optical arrangement (10) according to claim 7, wherein- the distance D between the first (1) and the second (2) mirror is equal to the sum of a focal length LI of the first mirror (1) and a focal length L2 of the second mirror (2) .

9. Optical arrangement (10) according to any one of the preceding claims, wherein- the third mirror (3) is an off-axis mirror.

10. Quantum computing arrangement (100) , comprising- an ion trap (20) configured to trap an ion crystal (6) of several ions (6' ) lined up along a predefined line (7) ,- the optical arrangement (10) according to any one of the preceding claims, wherein- the ion trap (20) and the optical arrangement (10) are arranged such that the trapped ion crystal (6) is located in a focal point (F3) of the third mirror (3) .

11. Quantum computing arrangement (100) according to claim10, wherein- the optical arrangement (10) is the one according to claim3 or any one of claims 4 to 9 in its dependency on claim 3,- the predefined line (7) is orthogonal to the second axes of the first (1) and the second (2) mirror.

12. Quantum computing arrangement (100) according to claim 10 or 11, further comprising- a laser (4) which is arranged such that the beam of the laser (4) is impinged onto the first mirror (1) .

13. Quantum computing arrangement (100) according to claim 12, wherein- the laser (4) , the optical arrangement (10) and the ion trap (20) are arranged such that, during operation, the predefined line (7) is parallel to the length axis of the elongated beam profile at the location of the ion crystal (6' ) .

14. Quantum computing arrangement (100) according to claim 12 or 13, wherein- the radiation of the laser (4) covers a wavelength range of at least 100 nm.

15. Quantum computing arrangement (100) according to any one of claims 10 to 14, further comprising- a vacuum chamber (30) , wherein- the ion trap (20) and the optical arrangement (10) are arranged in the vacuum chamber (30) .

16. Quantum computer (1000) , comprising - a quantum computing arrangement (100) according to any one of the claims 10 to 15 and configured for performing quantum computations .

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