Patent Publication Number: US-11651949-B2

Title: Spherical ion trap and trapping ions

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/144,066 (filed Feb. 1, 2021), which is herein incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention. 
    
    
     BRIEF DESCRIPTION 
     Disclosed is a spherical ion trap for trapping ions, the spherical ion trap comprising: a substrate comprising an electrical insulator and an ion aperture bounded by a substrate wall such that the ion aperture receives ions; a first RF electrode disposed on the substrate in electrostatic communication with an ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region and receives DC and RF voltage; a second RF electrode disposed on the substrate in electrostatic communication with the ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region, such that the second RF electrode is spaced apart from the first RF electrode, opposes the first RF electrode, and receives the DC and RF voltage; a plurality of RF ground electrodes disposed on the substrate in electrostatic communication with the ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region, such that the RF ground electrodes are spaced apart from each other and from the first RF electrode and the second RF electrode, and receive a DC voltage; and the ion trapping region bounded by opposing first RF electrode and second RF electrode and the RF ground electrodes, such that: the ion trapping region is disposed within the ion aperture and receives ions that are selectively trapped in the ion trapping region in response to receipt of the DC and RF voltage by the first RF electrode and the second RF electrode, and receipt of the DC voltages by the RF ground electrodes, and the first RF electrode, the second RF electrode, the RF ground electrodes, and the ion trapping region are disposed in the same plane within the ion aperture. 
     Disclosed is a process for trapping ions with a spherical ion trap, the process comprising: receiving, by an ion trapping region of a spherical ion trap, a plurality of ions, the spherical ion trap comprising: a substrate comprising an electrical insulator and an ion aperture bounded by a substrate wall such that the ion aperture receives the ions; a first RF electrode disposed on the substrate in electrostatic communication with an ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region and receives DC and RF voltage; a second RF electrode disposed on the substrate in electrostatic communication with the ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region, such that the second RF electrode is spaced apart from the first RF electrode, opposes the first RF electrode, and receives the DC voltage RF power; a plurality of RF ground electrodes disposed on the substrate in electrostatic communication with the ion trapping region and that protrudes from the substrate wall into the ion aperture toward the ion trapping region, such that the RF ground electrodes are spaced apart from each other and from the first RF electrode and the second RF electrode, and receive DC voltages; and the ion trapping region bounded by opposing first RF electrode and second RF electrode and the RF ground electrodes, such that: the ion trapping region is disposed within the ion aperture and receives ions that are selectively trapped in the ion trapping region in response to receipt of the DC and RF voltages by the first RF electrode and the second RF electrode, and receipt of the DC voltages by the RF ground electrodes, and the first RF electrode, the second RF electrode, the RF ground electrodes, and the ion trapping region are disposed in the same plane within the ion aperture; providing the first RF electrode and the second RF electrode with DC and RF voltage; providing the RF ground electrodes with the DC voltage; forming a trapping potential field in the ion trapping region by the DC and RF voltages; and trapping the ions in the ion trapping region in response to forming the trapping potential field from the DC and RF voltages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description cannot be considered limiting in any way. Various objectives, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings, in which like reference numerals identify like elements. 
         FIG.  1    shows a plan view of a first side of a spherical ion trap, according to some embodiments. 
         FIG.  2    shows a plan view of a second side of the spherical ion trap of  FIG.  1   , according to some embodiments. 
         FIG.  3    shows a cross-section of the spherical ion trap of  FIG.  1   , according to some embodiments. 
         FIG.  4    shows a plan view of a first side of a spherical ion trap, according to some embodiments. 
         FIG.  5    shows a plan view of a second side of the spherical ion trap of  FIG.  4   , according to some embodiments. 
         FIG.  6    shows a perspective view of the spherical ion trap of  FIG.  4   , according to some embodiments. 
         FIG.  7    shows a plan view of a first side of a spherical ion trap, according to some embodiments. 
         FIG.  8    shows a plan view of a second side of the spherical ion trap of  FIG.  7   , according to some embodiments. 
         FIG.  9    shows a cross-section of the spherical ion trap of  FIG.  7   , according to some embodiments. 
         FIG.  10    shows a plan view of a first side of a spherical ion trap, according to some embodiments. 
         FIG.  11    shows a plan view of a second side of the spherical ion trap of  FIG.  10   , according to some embodiments. 
         FIG.  12    shows a plan view of a first side of a spherical ion trap, according to some embodiments. 
         FIG.  13    shows a plan view of a second side of the spherical ion trap of  FIG.  12   , according to some embodiments. 
         FIG.  14    shows a cross-section of the spherical ion trap of  FIG.  12   , according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments is presented herein by way of exemplification and not limitation. 
     Conventional spherical RF Paul ion traps can include three-dimensional electrode structures to generate the electric fields for trapping ions or can include planar electrode structures that have low ion trapping efficiency. The original Paul ion trap is described in W. Paul,  Electromagnetic traps for charged and neutral particles , Rev. Mod. Phys. 62, 531 (1990), the disclosure of which is incorporated by reference in its entirety. Some conventional ion traps includes a ring electrode situated between two end-cap electrodes or a toroidal configuration. The spherical ion trap described herein overcomes technical deviancies of the conventional ion traps and provides a high ion trapping efficiency with a planar electrode structure that can be formed by microfabrication. 
     It has been discovered that the spherical ion trap described herein can be used for compact and field-deployable atomic clocks, among other applications. The spherical ion trap can include a single electrically insulating wafer that is micromachined with metal patterned over some portions of the wafer to form the trap electrodes. Relative to conventional spherical RF Paul ion traps, the spherical ion trap described herein provides a beneficial combination of high trapping efficiency and compatibility with microfabrication techniques, wherein the spherical ion trap can be mass produced at low unit cost and with very small geometrical imperfections. 
     Spherical ion trap  200  can selectively trap ions. In an embodiment, with reference to  FIG.  1   ,  FIG.  2   ,  FIG.  3   ,  FIG.  4   ,  FIG.  5   ,  FIG.  6   ,  FIG.  7   ,  FIG.  8   ,  FIG.  9   ,  FIG.  10   ,  FIG.  11   ,  FIG.  12   ,  FIG.  13   , and  FIG.  14   , spherical ion trap  200  includes: a substrate  201  including an electrical insulator and an ion aperture  213  bounded by a substrate wall  214  such that the ion aperture  213  receives ions; a first RF electrode  204  disposed on the substrate  201  in electrostatic communication with an ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212  and receives DC and RF voltage  225 ; a second RF electrode  205  disposed on the substrate  201  in electrostatic communication with the ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the second RF electrode  205  is spaced apart from the first RF electrode  204 , opposes the first RF electrode  204 , and receives the DC and RF voltage  225 ; a plurality of RF ground electrodes ( 206 ,  207 ,  208 ,  209 ) disposed on the substrate  201  in electrostatic communication with the ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the RF ground electrodes ( 206 ,  207 ,  208 ,  209 ) are spaced apart from each other and from the first RF electrode  204  and the second RF electrode  205 , and receive a DC voltage  224 ; and the ion trapping region  212  bounded by opposing first RF electrode  204  and second RF electrode  205  and the RF ground electrodes, such that: the ion trapping region  212  is disposed within the ion aperture  213  and receives ions that are selectively trapped in the ion trapping region  212  in response to receipt of the DC voltage RF power  225  by the first RF electrode  204  and the second RF electrode  205 , and receipt of the DC voltage  224  by RF ground electrodes, and the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed in the same plane within the ion aperture  213 . 
     A number, size, and shape of the RF ground electrodes can be selected to provide for adequate compensation of stray fields or to provide a tailored electrostatic potential of the ion trapping region  212 . 
     In an embodiment, with reference to  FIG.  7   ,  FIG.  9   ,  FIG.  10   , and  FIG.  14   , spherical ion trap  200  includes a first ancillary compensation electrode  218  in electrostatic communication with the ion trapping region  212  and that receives a first compensation DC voltage  228 . In an embodiment, with reference to  FIG.  8   ,  FIG.  9   ,  FIG.  11   , and  FIG.  14   , spherical ion trap  200  includes a second ancillary compensation electrode  219  in electrostatic communication with the ion trapping region  212  and that receives a second compensation DC voltage  228 . In an embodiment, the first ancillary compensation electrode  218  opposes the second ancillary compensation electrode  219  across the ion trapping region  212 , as shown in  FIG.  9    and  FIG.  14   . In an embodiment, first ancillary compensation electrode  218  and the second ancillary compensation electrode  219  are disposed out of the plane in which the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed. A size and shape of first ancillary compensation electrode  218  and the second ancillary compensation electrode  219  can be selected to provide for adequate compensation of stray fields or to provide a tailored electrostatic potential of the ion trapping region  212 . 
     In an embodiment, with reference to  FIG.  4   ,  FIG.  5   ,  FIG.  6   ,  FIG.  10   ,  FIG.  11   ,  FIG.  12   ,  FIG.  13   , and  FIG.  14   , spherical ion trap  200  includes a plurality of in-plane compensation electrodes (e.g.,  210 ,  211 ) in electrostatic communication with the ion trapping region  212  and that receives a compensation DC voltage  229 . The in-plane compensation electrodes (e.g.,  210 ,  211 ) are disposed in the plane in which the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed. A number of the in-plane compensation electrodes can be selected to provide for adequate compensation of stray electric fields or to provide a tailored electrostatic potential of the ion trapping region  212 . In an embodiment, with reference to  FIG.  4   , the in-plane compensation electrodes include a first in-plane compensation electrode  210  and a second in-plane compensation electrode  211 . In an embodiment, the first in-plane compensation electrode  210  and the second in-plane compensation electrode  211  protrude from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the first in-plane compensation electrode  210  is spaced apart from and opposes the second in-plane compensation electrode  211 . 
     A thickness of the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  can be sufficient to form the trapping potential field in the ion trapping region  212 . It is contemplated that the thickness of the individual electrodes independently can be from 50 μm to 10 mm, e.g., 300 μm. A length of the electrodes ( 204 - 211 ) can be selected based on a size of the ion trapping region  212  desired in consideration of the size (e.g., radius) of the ion aperture  213 . It should be appreciated that ion aperture  213  provides for communication of ions that are transmitted through ion aperture  213 . 
     Some of the figures show disposal of electrical wiring trace  217  that connects electrical contact pad  216  to a certain electrode (e.g.,  204 - 211 ) via electrical wiring trace  217 . The electrical contact pad  216  can electrically interconnect an electrode (e.g., one of  204 - 211 ) to an power source such as DC voltage source  220  or DC and RF voltage source  221 , as shown in  FIG.  12   , FIG.  13 , or  FIG.  14   . In this manner, DC voltage source  220  can provide various independent DC voltage  224  (e.g.,  224 . 1 ,  224 . 2 ,  224 . 3 ,  224 . 4 ,  224 . 5 ) via voltage transmission lines  226  to RF ground electrode  206 , RF ground electrode  207 , RF ground electrode  208 , RF ground electrode  209 , in-plane compensation electrode  210 , in-plane compensation electrode  211 , first ancillary compensation electrode  218 , or second ancillary compensation electrode  219 , wherein the voltage waveforms (of e.g.,  224 . 1 ,  224 . 2 ,  224 . 3 ,  224 . 4 ,  224 . 5 ) can be selected in view of the desired ion trapping conditions. Moreover, DC and RF voltage source  221  can provide RF transmission line  227  via RF transmission line  227  to first RF electrode  204  and second RF electrode  205 , wherein the waveforms of RF transmission line  227  can be selected in view of the desired ion trapping conditions, e.g., a mass-to-charge, shape or size of ion trapping region  212 , and the like. 
     Elements of spherical ion trap  200  can be made of a material that is physically or chemically resilient in an environment in which spherical ion trap  200  is disposed. Exemplary materials include a metal, ceramic, thermoplastic, glass, semiconductor, and the like. Some of the elements of spherical ion trap  200  can be made of the same or different material and can be monolithic in a single physical body or can be separate members that are physically joined. 
     Spherical ion trap  200  can be made in various ways. It should be appreciated that spherical ion trap  200  includes a number of electrical or mechanical components, wherein such components can be interconnected and placed in communication (e.g., optical communication, electrical communication, mechanical communication, fluid communication, and the like) by physical, chemical, or mechanical interconnects. The components can be disposed on mounts that can be disposed on a bulkhead for alignment or physical compartmentalization. As a result, spherical ion trap  200  can be disposed in a terrestrial environment or space environment. Elements of spherical ion trap  200  can be formed from silicon, aluminum nitride, diamond, and the like although other suitable materials, such ceramic, glass, or metal can be used. According to an embodiment, the elements of spherical ion trap  200  are formed using semiconductor microfabrication techniques although the elements of spherical ion trap  200  can be formed using other methods, such as  3 D printing, injection molding, or machining a stock material such as block of material that is subjected to removal of material such as by cutting, laser ablation, and the like. Accordingly, spherical ion trap  200  can be made by additive or subtractive manufacturing. In an embodiment, elements of spherical ion trap  200  are selectively etched to remove various different materials using different etchants and photolithographic masks and procedures. The various layers thus formed can be subjected to joining by bonding to form spherical ion trap  200 . 
     In an embodiment, spherical ion trap  200  is fabricated by cutting the shape shown, e.g., in  FIG.  4   , out of a single electrically insulating wafer and patterning metal electrodes onto the areas each electrode. Cutting can be performed using laser machining, chemical etching, ion milling, or other microfabrication techniques. Metal patterning can be performed, e.g., by shadow masked sputtering or evaporation. 
     Spherical ion trap  200  has numerous advantageous and unexpected benefits and uses. In an embodiment, a process for trapping ions includes: receiving, by an ion trapping region  212  of a spherical ion trap  200 , a plurality of ions, the spherical ion trap  200  including: a substrate  201  including an electrical insulator and an ion aperture  213  bounded by a substrate wall  214  such that the ion aperture  213  receives the ions; a first RF electrode  204  disposed on the substrate  201  in electrostatic communication with an ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212  and receives DC and RF voltage  225 ; a second RF electrode  205  disposed on the substrate  201  in electrostatic communication with the ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the second RF electrode  205  is spaced apart from the first RF electrode  204 , opposes the first RF electrode  204 , and receives the DC and RF voltage  225 ; a plurality of RF ground electrodes disposed on the substrate  201  in electrostatic communication with the ion trapping region  212  and that protrudes from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the RF ground electrodes are spaced apart from each other and from the first RF electrode  204  and the second RF electrode  205 , and receive a DC voltage  224 ; and the ion trapping region  212  bounded by opposing first RF electrode  204  and second RF electrode  205  and the RF ground electrodes, such that: the ion trapping region  212  is disposed within the ion aperture  213  and receives ions that are selectively trapped in the ion trapping region  212  in response to receipt of the DC voltage RF power  225  by the first RF electrode  204  and the second RF electrode  205 , and receipt of the DC voltage  224  by RF ground electrodes, and the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed in the same plane within the ion aperture  213 ; providing the first RF electrode  204  and the second RF electrode  205  with DC and RF voltage  225 ; providing the RF ground electrodes with the DC voltage  224 ; forming a trapping potential field in the ion trapping region  212  by the DC and RF voltage  225  and the DC voltage  224 ; and trapping the ions in the ion trapping region  212  in response to forming the trapping potential field from the DC and RF voltage  225  and the DC voltage  224 . 
     The process for trapping ions can include tuning the trapping potential field to trap ions having a selected mass-to-charge ratio in the ion trapping region  212  and destabilizing trajectories of other ions that do not have the selected mass-to-charge ratio, resulting in the other ions not being trapped in the ion trapping region  212 . 
     In the process for trapping ions, the spherical ion trap  200  can include a first ancillary compensation electrode  218  in electrostatic communication with the ion trapping region  212 , such that the first ancillary compensation electrode  218  receives a first compensation DC voltage  228 ; and the process can include providing the first compensation DC voltage  228  to the first ancillary compensation electrode  218  to trap ions in the ion trapping region  212 . 
     In the process for trapping ions, the spherical ion trap  200  can include a second ancillary compensation electrode  219  in electrostatic communication with the ion trapping region  212  and that receives a second compensation DC voltage  228 ; the first ancillary compensation electrode  218  opposes the second ancillary compensation electrode  219  across the ion trapping region  212 ; and the process can include providing the second shielding DC voltage  228  to the second ancillary compensation electrode  219  to trap ions in the ion trapping region  212 . 
     In the process for trapping ions, the first ancillary compensation electrode  218  and the second ancillary compensation electrode  219  can be disposed out of the plane in which the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed. In the process for trapping ions, the spherical ion trap  200  can include a plurality of in-plane compensation electrodes  210  in electrostatic communication with the ion trapping region  212  and that receives a compensation DC voltage  229 ; and the process can include providing the compensation DC voltage  229  to the in-plane compensation electrodes  210  to trap ions in the ion trapping region  212 . 
     In the process for trapping ions, the in-plane compensation electrodes can be disposed in the plane in which the first RF electrode  204 , the second RF electrode  205 , the RF ground electrodes, and the ion trapping region  212  are disposed. The in-plane compensation electrodes can include comprise a first in-plane compensation electrode  211  and a second in-plane compensation electrode  211 . The first in-plane compensation electrode  210  and the second in-plane compensation electrode  211  can protrude from the substrate wall  214  into the ion aperture  213  toward the ion trapping region  212 , such that the first in-plane compensation electrode  210  is spaced apart from and opposes the second in-plane compensation electrode  211 . 
     In an embodiment, a process for trapping ions with spherical ion trap  200  includes, applying a radiofrequency voltage to first RF electrode  204  and second RF electrode  205 , while the other electrodes ( 206 - 211 ,  218 ,  219  if present) are electrically grounded or held at DC voltages for compensation of stray electric fields present in the environment. Here, the ratios of the secular motion frequencies along the three principal axes are determined by the geometry of the electrodes near the position of the ion and the DC and RF voltages, and can be set within a wide range to optimize performance for the specific application. The ion(s) is trapped at the geometric center of the electrodes. 
     Spherical ion trap  200  is advantageous over conventional three-dimensional spherical Paul traps since spherical ion trap  200  can be microfabricated so that spherical ion trap  200  can be mass produced at low unit cost. The RF electrodes  204  and  205  are technically superior to conventional machined three-dimensional spherical Paul traps since machining imperfections can be much smaller with microfabrication than with conventional machining, and machining imperfections can lead to deviations from the desired principal axis directions and secular frequencies as well as excess micromotion. The spherical ion trap  200  may be technically superior to conventional planar spherical Paul traps since spherical ion trap  200  has high trapping efficiency so that lower voltages are used for operation, which provides reductions in the size, weight, and power of deployed systems using the spherical ion trap  200  as compared with conventional ion traps. 
     While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined. 
     All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like. 
     As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements. 
     All references are incorporated herein by reference. 
     The use of the terms “a,” “an,” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such. 
     The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances.