Quantum processor, method of trapping ions, and method of manipulating ions

Abstract

According to the present invention, there is provided a quantum processor comprising: a substrate having a first surface, a first module having an upper surface and a lower surface and having a plurality of electrodes formed on the upper surface, each electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the first module, and a second module having an upper surface and a lower surface and having a plurality of electrodes formed on the upper surface, each electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the second module, the second module being a first distance in a first direction from the first module and a controller. The substrate comprises a plurality of substrate electrodes formed on its first surface and located at least between the first module and the second module, the electrodes being electrically coupled to a substrate signal generator configured to output a radio frequency signal to create an ion trap above a space between the first module and the second module, and the controller is configured to control the signal generator.

Description

[Technical Field]

[0001] The present invention relates to providing a modular system for an ion trap quantum computer. [Background technology]

[0002] Unlike commonly referred to as "classical computing," quantum computing relies on the quantum mechanical properties of particles or matter to produce or modify data. Data can be represented by quantum bits or "qubits," which are two-state quantum mechanical systems. Unlike classical computing, qubits can be in a superposition of quantum states. Another feature of quantum computing is entanglement between qubits, where the state of one particle or atom is affected by the state of another particle or atom.

[0003] Quantum mechanical qubits can simultaneously encode information as combinations of zeros and ones. Such properties enable many complex numerical applications that have traditionally been difficult with classical computers. Examples include artificial intelligence, image processing and recognition, cryptography, or secure communications.

[0004] Within the ionic hyperfine electron states (Zeeman split states) can be revealed by the use of magnetic fields and different electronic levels used as different qubit states, and electrons moving between levels using microwave radiation or lasers.

[0005] There can be multiple quantum gates on a single chip, or module. For example, a module measuring 300 x 300 mm can have 4,096 gate zones. However, there is a limit to the size of individual modules that can be easily manufactured. Therefore, one solution is to create an array of modules, with a spacing of a few micrometers between each module, as shown in Figure 1. Ions, or qubits, can be transferred between different modules as needed, thus enabling the development of significantly larger computers. For example, a 10 x 10 module array could have 409,600 different gate zones.

[0006] However, one drawback of using multiple modules is that ions must be shuttled between modules, which can be problematic, especially if there is misalignment between the modules. It can be difficult to position the modules close enough to each other so that there is no energy barrier between the modules that ions must overcome. If there is an energy barrier, it can be difficult to move ions between modules. Furthermore, if ions overcome the energy barrier and move between modules, additional thermal noise will be generated.

[0007] It is therefore desirable to create an arrangement that can shuttle ions between modules. Summary of the Invention

[0008] It is an object of the present invention to provide a method for manufacturing a scalable system in which the transport of ions between modules is seamless.

[0009] Therefore, in accordance with the present invention, there is provided a substrate having a first surface; a first module affixed to the substrate, having upper and lower surfaces, and having a surface linear Paul trap with a plurality of electrodes formed on the upper surface, each RF electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the first module; and a second module affixed to the substrate, spaced apart from the first module, having upper and lower surfaces, and having a surface linear Paul trap with a plurality of electrodes formed on the upper surface, each RF electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the second module, the second module being spaced a first distance in a first direction from the first module and a controller; the substrate comprising a surface linear Paul trap with a plurality of substrate electrodes formed on its first surface and located at least within the space between the first module and the second module, the RF electrodes electrically coupled to a substrate signal generator configured to output a radio frequency signal to create an ion trap above the space between the first module and the second module, and a controller configured to control the signal generator.

[0010] The substrate electrode thus generates a radio frequency field above the substrate such that ions can be shuttled along a minimum energy path. The electromagnetic field generated by the radio frequency electrode confines ions in a second direction perpendicular to the first direction and in a third direction parallel to the first and second directions. The ion trap above the substrate thus forms a continuous ion trap path between the ion trap above the first module and the ion trap above the second module.

[0011] The first module and the second module have a space therebetween, and the substrate ion trap is formed above the substrate in the space between the first module and the second module, and the first surface of the substrate is at a different height than the top surfaces of both the first module and the second module.

[0012] The signal generators coupled to the module electrodes and the signal generators coupled to the substrate electrodes are preferably configured to output the same radio frequency so that the electromagnetic fields generated by the electrodes are all similar. There may be a single signal generator, or there may be one or more signal generators for the module electrodes and one or more signal generators for the substrate electrodes, but they are configured to output the same radio frequency.

[0013] Adjacent to the edge of the module, in a second direction perpendicular to the first direction and within the plane of the module, the plurality of electrodes on each of the first and second modules have a first length, and the plurality of electrodes on the substrate have a second length in the second direction, the second length being at least 10% greater than the first length. This may be at least 50% greater. Substrate electrodes having a different width than the module electrodes mean that confining potentials can be generated at different locations. Because the top of the substrate is at a lower height than the top of the module, the substrate electrodes must generate a confining field at a higher position to generate an ion path at a similar height as the ion path above the module.

[0014] The substrate RF electrode extends between the first module and the second module. In particular, the substrate occupies at least 80%, preferably at least 90%, of the first distance between the first module and the second module. By extending the electrode across substantially the entire distance between the modules, a continuous ion path can be created. Preferably, the electrode extends across the entire distance between the modules.

[0015] The controller may be configured to control a signal generator coupled to the module electrodes to generate a module radio frequency field that creates an ion trap with a time-averaged energy depth of x, and to control a signal generator coupled to the substrate electrodes to generate a substrate radio frequency field between the ion trap above the first module and the ion trap above the second module, wherein the maximum energy barrier on the continuous ion trap path between the first module and the second module is less than x. Thus, there is a continuous ion path from above the first module to above the second module.

[0016] Preferably, the maximum energy barrier is less than x / 10, more preferably less than x / 100. In absolute terms, the energy barrier is preferably less than 10 meV, more preferably less than 1 meV.

[0017] The RF potential applied to the substrate electrode preferably has a greater amplitude than the RF potential applied to the module electrode.

[0018] By providing channels between the modules, the distance between the modules can be made larger. In particular, a distance of at least 5 μm can be achieved. The distance between the first module and the second module can be less than 1 mm.

[0019] The first and second modules may further comprise a second set of electrodes, each coupled to a signal generator configured to output a DC signal. These second sets of electrodes enable the generation of a potential well in which ions can be confined. These electrodes confine ions in a first direction. Thus, the first set of electrodes (which generate the RF field) confine ions in the second and third directions, and the second set of electrodes confine ions in the first direction.

[0020] The substrate may also further comprise a second set of electrodes, each coupled to a signal generator configured to output a DC signal.

[0021] The first module may be attached by its lower surface to the first surface of the substrate, and the second module is attached by its lower surface to the first surface of the substrate, so that the modules are on top of the substrate.

[0022] One or more of the signal generators may comprise a DAC.

[0023] According to the present invention, there is provided a method of trapping ions on a device comprising a first module and a second module affixed to a substrate, the second module being spaced a first distance in a first direction from the first module, the first module and the second module each having a surface linear Paul trap comprising a first set of module electrodes, each configured to output a radio frequency signal and coupled to a signal generator having a second set of module electrodes, each coupled to a signal generator configured to output a DC signal, the substrate being located within a space between at least the first module and the second module and comprising a surface linear Paul trap including a plurality of substrate electrodes, each substrate electrode coupled to a signal generator configured to output a radio frequency signal. The method includes generating a radio frequency signal using a first set of module electrodes of a first module and a second module to create an ion trap above the first module and an ion trap above the second module, the ion traps having a time-averaged energy depth of x; generating a radio frequency signal of the same frequency using substrate electrodes to create a continuous ion trap path above the substrate between the ion trap above the first module and the ion trap above the second module, the maximum energy on the continuous ion trap path being less than x; and trapping ions in at least one of the ion traps.

[0024] According to the present invention there is further provided a method of manipulating ions, including a method of trapping ions as described above, comprising generating a potential well above a first module using electrodes coupled to a signal generator configured to generate a DC signal; trapping ions at an intersection of the potential well and an ion trap generated by the radio frequency signal; and generating a series of signal generator signals to electrodes on the first module and a second module to move ions from the ion trap above the first module, into a continuous ion trapping path above the substrate, and into the ion trap above the second module.

[0025] A signal generator coupled to the module electrodes preferably generates a module radio frequency field that creates an ion trap having a time-averaged energy depth of x, and a signal generator coupled to the substrate electrodes preferably generates a substrate radio frequency field between the ion trap above the first module and the ion trap above the second module, and the maximum energy barrier on the ion trap series path between the first module and the second module is less than the time-averaged energy depth x. [Brief explanation of the drawings]

[0026] [Figure 1] Figure 1 shows the array of modules in a quantum computer. [Figure 2] FIG. 2 shows a portion of the module. [Figure 3] FIG. 3 shows a substrate according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring to FIG. 1, an exemplary arrangement of multiple modules 10 within a quantum computer is shown. An example of a portion of a module is shown in FIG. 2, which illustrates a surface linear Paul trap. The module includes multiple electrodes to which a voltage can be applied to form a potential well for trapping ions. Some of the electrodes 12 are RF electrodes controlled by one or more DACs 17 that generate an RF field. There may be a separate DAC 17 for each electrode, or one DAC 17 may control several electrodes 12. While coupled to the electrodes, the DACs may be remote. The RF field generated by these electrodes creates an ion trap in which ions are positioned at minimum energy and confined by energy barriers in the y and z directions. Thus, the generated RF field confines ions in the y and z directions as shown in the figure. Thus, the RF field generated by the multiple RF electrodes creates a minimum-energy path in the x direction along which ions can travel.

[0028] The RF electrode 12 and associated DAC 17 generate a radio frequency field having a time-averaged energy depth. As an example, for an RF DAC generating an amplitude of 200V at 20 MHz with a height of 125 μm, for Yb171 ions, the time-averaged energy depth is 500 meV.

[0029] Additionally, there is a DC electrode 11 configured to generate a DC electromagnetic field and controlled by a DAC 16. The DAC 16 is coupled to the electrode 11, and as shown in FIG. 2, the DAC is often located remotely from the DC electrode simply due to space constraints. There may be a different DAC for each electrode, or a DAC may control multiple electrodes. Different DC voltages can be applied to different electrodes to create potential wells in which ions are located. As the DC voltages of the different electrodes are varied, ions move in the x-direction along the path of least energy. Thus, the combination of the RF electrode 12 and the DC electrode 11 controls the position of the ions. Thus, ions may be moved above the module as desired.

[0030] As can be seen in Figure 2, both the RF and DC electrodes are adjacent to the edge of the module in a first direction, in particular they abut the edge of the module.

[0031] According to the present invention, modules are arranged on a substrate 20, as shown in FIG. 3. Between the modules are multiple RF electrodes 22, each coupled to a DAC 27 configured to output radio frequency waves. Like the modules, the RF electrodes form a surface linear Paul trap. The DAC 27 preferably outputs the same radio frequency waves as the DAC 17 that controls the RF electrodes on the substrate. The RF electrodes on the substrate generate an RF field above the substrate, with a minimum energy path surrounded by an energy barrier. If the minimum energy path is smaller than the trap depth (time-averaged energy depth) above the modules, then ions can pass above the substrate between the modules.

[0032] The minimum energy path above the substrate must be smaller than the time-averaged energy depth above the module. However, it is preferable for the minimum energy path to have as low an energy as possible to reduce heating. Preferably, the maximum energy level on the minimum energy path is less than 1 meV, which would be similar to the energy of the junctions on the module. Furthermore, to reduce heating, the potential energy gradient on the minimum energy path must be minimized.

[0033] All of the DACs may be controlled by a controller 50, which controls the voltages generated by each DAC.

[0034] Because the RF electrodes 22 on the substrate are at a different height than the RF electrodes 12 on the modules, electromagnetic fields of different strengths may be applied so that the minimum energy path above the substrate is at a similar height as the ion path above the substrate. Different electromagnetic field strengths can be achieved by applying a larger voltage (at the same RF frequency) and / or by using wider electrodes in the y-direction, i.e., in the plane of the substrate but perpendicular to the minimum distance between modules. By having the minimum energy path at a similar height, a continuous path is created between the ion traps above adjacent modules.

[0035] Calculating the height of the ion trap above the electrodes is well known and is given by:

[0036]

number

[0037] where z0 is the height of the electric field minimum, a is the width of the central DC electrode, and b and c are the widths of the rf electrodes. Calculation of ion height is described in detail in "Analytic model for electrostatic fields in surface-electrode ion traps," MG House Physical Review A 78 033402, September 2, 2008, the contents of which are incorporated herein. Therefore, the position of the minimum energy above the substrate can be controlled by the width of the electrodes. Therefore, the position of the minimum energy above the substrate can be controlled to a similar (absolute) height as the minimum energy of the ion trap above the module.

[0038] If the heights of the minimum energy locations above the substrate and the modules are similar, then a minimum energy path is connected; this well-known concept is used in "T-junction ion trap array for two-dimensional ion shuttling, storage and manipulation," WK Hensinger et al., Applied Physics Letters 88, 034101, January 17, 2006; and "High-Fidelity Transport of Trapped-Ion Qubits through an X-Junction Trap Array," Blakestad et al., Physical Review letters 16 April 2009, the contents of both of which are incorporated herein. Thus, by creating an ion trap above the substrate, the minimum energy path between two modules is connected, providing a continuous path between the modules along which ions can be transferred.

[0039] The RF electrodes on the substrate preferably occupy the distance between the first and second modules. In particular, they occupy at least 80%, or preferably at least 90%, of the distance in the first direction between the modules. Preferably, they occupy the entire distance in the first direction between the modules.

[0040] In particular, the height of the ion path between modules should not be below the level of the top surface of the modules. This is controlled by a controller that controls the RF DAC 27 to generate an electromagnetic field such that the minimum energy path above the substrate is at a height (from the surface of the substrate) that is greater than the height of the modules. Therefore, the height of the minimum energy path above the substrate is greater than the height of the modules. Preferably, the height of the minimum energy path above the substrate is substantially equal to the height of the modules plus the height of the minimum energy path above the modules.

[0041] As can be seen in Figure 3, the width of the substrate RF electrodes 22 in the y-direction, i.e., in the plane of the substrate but perpendicular to the shortest distance between modules, is greater than the width of the module RF electrodes. In particular, they are preferably at least 10% greater. For example, they may be twice as wide. The greater the electrode width, the greater the height of the minimum energy path above the substrate.

[0042] As described above, the RF field above the module creates an ion trap with a time-averaged energy depth of x. The lowest energy path is created above the substrate by the substrate RF electrodes, and according to the present invention, the maximum barrier on the ion trap path above the substrate and between modules is less than x. Therefore, when a change in potential by the DC electrodes moves trapped ions above the substrate, the energy barrier is less than the ion trap depth above the module. The maximum energy barrier in the continuous bath should preferably be as low as possible, preferably less than x / 10, more preferably less than x / 100. In absolute terms, the maximum energy barrier should be less than 10 meV. At less than 1 meV, the energy barrier is smaller than the energy experienced by ions passing through the junction.

[0043] The ion trap created above the substrate also has a time-averaged energy depth. To make the time-averaged energy depth above the substrate similar to the time-averaged energy depth above the module, the radio frequency potential applied to the substrate electrode has a larger amplitude than the radio frequency potential applied to the module electrode. Preferably, the time-averaged energy depth above the substrate is within 20% of the time-averaged energy depth above the module.

[0044] Just as the RF and DC electrodes on the modules abut the edges of the modules, the RF and DC electrodes on the substrate also abut the edges of the modules, helping to achieve a continuous path between modules with the lowest possible maximum energy barrier.

[0045] The device described above uses RF module electrodes of the first and second modules to generate radio frequency signals to generate ion traps above the first and second modules, the ion traps having a time-averaged energy depth of x. A radio frequency signal of the same frequency is generated by a substrate RF electrode to generate a continuous ion trap path above the substrate between the ion trap above the first module and the ion trap above the second module. The maximum energy along the continuous ion trap path is less than the time-averaged energy depth above the first or second module. A potential well is generated above the first module using a DC electrode coupled to a DAC configured to generate a DC signal, which traps ions at the intersection of the potential well and the ion trap generated by the radio frequency signal. A series of DAC signals to the DC electrodes on the first module, the substrate, and the second module is generated to move ions from the ion trap above the first module along the continuous ion trap path above the substrate and onto the ion trap above the second module.

[0046] Although the above arrangement is described using a DAC, any form of signal generator may be used.

[0047] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0048] As used herein, "and / or" should be taken as a specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" should be taken as a specific disclosure of (i) A, (ii) B, and (iii) each of A and B, as if each were set forth individually herein.

[0049] Unless the context dictates otherwise, the above feature descriptions and definitions are not limited to any particular aspect or embodiment of the invention, but apply equally to all aspects and embodiments described.

[0050] Those skilled in the art will further appreciate that although the present invention has been described by way of example with reference to certain embodiments, it is not limited to the disclosed embodiments, and alternative embodiments may be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. 1. A quantum processor, comprising: a substrate having a first surface; a first module affixed to the substrate, the first module having an upper surface and a lower surface, the first module including a surface linear Paul trap with a plurality of electrodes formed on the upper surface, each electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the first module; a second module affixed to the substrate and spaced apart from the first module, the second module having an upper surface and a lower surface, the second module having a surface linear Paul trap with a plurality of electrodes formed on the upper surface, each electrode coupled to a signal generator configured to output a radio frequency signal to create an ion trap above the second module, the second module being spaced a first distance in a first direction from the first module; a controller; a surface linear Paul trap, the substrate comprising a plurality of substrate electrodes formed on a first surface thereof and positioned at least within the space between the first module and the second module, the electrodes electrically coupled to an equipment signal generator configured to output a radio frequency signal to generate an ion trap above the space between the first module and the second module, and the controller configured to control the signal generator;

2. 10. The processor of claim 1, wherein the signal generator coupled to the module electrode and the signal generator coupled to the substrate electrode are configured to output the same radio frequency signal.

3. 10. The processor of claim 9, wherein the ion trap above the substrate forms a continuous ion trap path between the ion trap above the first module and the ion trap above the second module.

4. 10. The processor of claim 1, wherein the controller is configured to control the signal generator coupled to the substrate electrode and the signal generator coupled to the module electrode such that the continuous path does not fall below the level of the top surface of the module.

5. 10. The processor of claim 9, wherein the plurality of electrodes on each of the first and second modules have a first length adjacent the edge of the module in a second direction perpendicular to the first direction and within the plane of the module, and the plurality of electrodes on the substrate have a second length in the second direction, the second length being at least 10% greater than the first length.

6. 10. The processor of claim 9, wherein the controller is configured to control the signal generator coupled to the module electrodes to generate a module radio frequency field that creates an ion trap with a time-averaged energy depth of x, and to control the signal generator coupled to the substrate electrodes to generate a substrate radio frequency field between the ion trap above the first module and the ion trap above the second module, wherein a maximum energy barrier on a continuous path of ion traps between the first module and the second module is less than the time-averaged energy depth of x.

7. The processor of claim 6 or claim 7, wherein the maximum energy barrier is less than 10 meV.

8. 10. A processor according to any one of the preceding claims, wherein the RF potential applied to the substrate electrode has a greater amplitude than the RF potential applied to a module electrode.

9. 10. A processor according to any one of the preceding claims, wherein the module electrodes are coupled to a module signal generator and the substrate electrodes are coupled to a substrate signal generator.

10. 10. The processor of claim 1, wherein the first module and the second module further comprise a second set of the electrodes, each coupled to a signal generator configured to output a DC signal.

11. 10. The processor of any one of the preceding claims, wherein the substrate further comprises a second set of substrate electrodes, each coupled to a signal generator configured to output a DC signal.

12. 10. A processor according to any one of the preceding claims, wherein the first module is attached by its lower surface to the upper surface of the substrate and the second module is attached by its lower surface to the upper surface of the substrate.

13. 10. A processor according to any one of the preceding claims, wherein the substrate electrode extends the entire distance between the first module and the second module.

14. 1. A method of trapping ions on a device comprising a first module and a second module mounted on a substrate, the second module being spaced a first distance in a first direction from the first module, the first and second modules each having a surface linear Paul trap with a first set of module electrodes, each configured to output a radio frequency signal and coupled to a signal generator having a second set of module electrodes, each coupled to a signal generator configured to output a DC signal, the substrate being located in the space between at least the first module and the second module and comprising a plurality of substrate electrodes, each substrate electrode coupled to a signal generator configured to output a radio frequency signal, the method comprising: generating a radio frequency signal using a first set of module electrodes of the first module and the second module to create an ion trap above the first module and an ion trap above the second module, the ion traps having a time-averaged energy depth of x; generating a radio frequency signal at the same frequency using the substrate electrode to create a continuous ion trapping path above the substrate between the ion trap above the first module and the ion trap above the second module, wherein the maximum energy along the continuous ion trapping path is less than x; trapping ions in at least one of said ion traps.

15. 10. A method of manipulating ions, comprising the method of trapping ions according to claim 1, generating a potential well above the first module using the electrodes coupled to the signal generator configured to generate a DC signal, wherein trapping ions includes trapping them at an intersection of the potential well and the ion trap generated by the wireless high frequency signal; generating a series of signal generator signals to the electrodes on the first module and the second module to move the ions from the ion trap above the first module, into the continuous ion trapping path above the substrate, and onto the ion trap above the second module.

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