DETECTION SCHEME

Description

Technical Field

[0001] Embodiments described herein generally relate to quantum computing.Background

[0002] Quantum computing may be used to perform advanced computational processing. Quantum computing may leverage physical properties of quantum bits (e.g., qubits), such as quantum superposition and quantum entanglement. For example, in contrast with conventional digital processing in which data is encoded into binary states (e.g., 1 or 0), quantum superposition enables the qubits used in quantum computing to be in both states simultaneously. In contrast with the independent nature of individual bits in conventional digital processing, quantum entanglement enables a linking between or among qubits so each qubit may provide information about related qubits. Schneider in "Optical Frequency Standard with a single 171Yb+ ion" (https: / / d-nb.info / 977243176 / 34) describes an electric quadrupole transition in a single 171< Yb +< laser-cooled ion stored in a radio frequency Paul trap for potential use as optical frequency standard to replace an atomic frequency standard. Keselmann et al in "High fidelity state detection and tomography of a single ion Zeeman qubit" (2011.03.27; XP 080546292) describe high-fidelity Zeeman qubit state detection in a single trapped 88< Sr +< ion for use in fault-tolerant computation or high-precision quantum process tomography. Schacht et al. in "171Yb+ System Stability, 5D3 / 2 Hyperfine State Detection Efficiency and F=2 Lifetime" (2013.10.09) discloses a data acquisition system that is designed to stabilize cooling and probe rates to maximize detection sensitivity in the context of a 171Yb+ ion. However, the fidelity of data encoded into the qubits is subject to errors, such as a spontaneous state change of qubits. What is needed in an improved solution to improve qubit fidelity.Brief Description of the Drawings

[0003] FIG. 1 is a first 171Yb+ state transition diagram, according to an embodiment. FIG. 2 is a second 171Yb+ state transition diagram, according to an embodiment. FIG. 3 is a 171Yb+ state transition method, according to an embodiment. FIGs. 4A-4F are 171Yb+ states, according to an embodiment. FIG. 5 is a block schematic diagram of a computer system to implement ytterbium shelving detection, according to an example embodiment. Description of Embodiments

[0004] The present subject matter provides technical solutions for the technical problems facing quantum computing by improving the accuracy and precision of qubit readout. As used herein, qubit readout refers includes determining which logical state the qubit was in following execution of a particular computation. For ionized ytterbium-171 (i.e., 171Yb+) hyperfine qubits, qubit readout is achieved by identifying a qubit state that emits many photons as "bright" and a qubit state that emits few or no photons as "dark." By collecting photons from the qubit, the state of the qubit can be determined. However, the readout fidelity of 171Yb+ qubits is reduced by mixing of the bright and dark states, which creates ambiguity when determining the state of the qubit. In an embodiment, improving readout fidelity of 171Yb+ qubits may improve fidelity by an order of magnitude, such as by improving readout fidelity from 99.9% to 99.99%. This improvement in detection fidelity may substantially increase the computational power of a quantum computer.

[0005] Technical solutions described herein improve the readout fidelity by reducing the ambiguity between the bright and dark states. In an embodiment, this includes transferring the qubit population that is in the dark quantum state to an auxiliary third state. The auxiliary third state remains dark and reduces the mixing between the logical bright and dark states. This process uses multiple laser pulses to ensure high fidelity population transfer, thus preserving the dark nature of the dark state during readout. This transfer to an auxiliary third state may be referred to as "shelving." While 171Yb+ qubits offer various advantages described herein, the atomic structure of 171Yb+ qubits may be considered unfavorable for shelving. However, using the controlled state transitions described herein, shelving 171Yb+ qubits may provide improved readout fidelity.

[0006] The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to understand the specific embodiment. Other embodiments may incorporate structural, logical, electrical, process, and other changes.

[0007] FIG. 1 is a first 171Yb+ state transition diagram 100, according to an embodiment. Diagram 100 shows various 171Yb+ states and state transitions. As shown in diagram 100, straight lines indicate transitions at least partially driven by lasers, wavy lines indicate decay transitions, transition line thickness indicates transition strength, dashed lines indicate undesired transitions that are detrimental to detection, and solid lines are desirable or inconsequential transitions in state detection.

[0008] Laser transition 110 may include a laser applied to transition states from a dark S-state 135 to a P-state 140, which may be detrimental to detection. Laser transition 115 may include a laser applied to transition states from a bright S-state 130 to the P-state 140, which may be beneficial in state detection. Decay transition 120 may include a spontaneous 171Yb+ state decay from P-state 140 to bright S-state 130, which may be beneficial in state detection. Decay transition 125 may include a spontaneous 171Yb+ state decay from P-state 140 to dark S-state 135, which may be detrimental in state detection. Light is collected from the decay transition 120. The decay transition 125 is undesirable, and may typically occur after approximately 3 ms. The laser transition 110 is also undesirable, and may typically occur after approximately 52 ms.

[0009] Decay transition 150 may include a spontaneous 171Yb+ state decay from P-state 140 to bright D-state 160, which may be inconsequential in state detection. Decay transition 155 may include a spontaneous 171Yb+ state decay from P-state 140 to dark D-state 165, which may be inconsequential in state detection. Laser transition 170 may include a laser applied to transition states from a bright D-state 165 (e.g., through an unshown intermediary state such as 2< [3 / 2] 1 / 2 ) to bright S-state 130, which may be beneficial in state detection. Laser transition 175 may include a laser applied to transition states from bright D-state 160 (e.g., through an unshown intermediary state such as 2< [3 / 2] 1 / 2 ) to bright S-state 130, which may be beneficial in state detection. Both decay transition 150 and decay transition 155 are both returned to bright S-state 130, and may be considered inconsequential for state detection.

[0010] FIG. 2 is a second 171Yb+ state transition diagram 200, according to an embodiment. This second 171Yb+ state transition diagram 200 is similar to diagram 100 with a few notable differences. In diagram 200, laser transitions 205 between S-state 235 and D-state 260 are used before collecting light (e.g., detecting bright or dark state) to transfer any 171Yb+ ions from S-state 235 to dark D-state 260. Light is collected from decay transitions 220 and 225 from P-state 240 to dark S-states 230 and 235. For any 171Yb+ ions that decay from P-state 240 to dark S-state 235, laser transition 210 is used to transition the ions back from dark S-state 235 to P-state 240. The decay transition 275 from dark D-state 260 to bright S-state 230 is undesirable and may occur after approximately 53 ms. Similarly, the decay transition 250 from P-state 240 to dark D-state 260 is undesirable and may occur after approximately 100 ms. However, both of these undesirable state transitions are substantially slower than the 3 ms decay transition 125 in diagram 100. The laser and decay transitions shown in diagram 200 thus increases bright state lifetime by allowing 14.7 GHz sidebands and provides fast and efficient repump with no additional laser overhead.

[0011] FIG. 3 is a 171Yb+ state transition method 300, according to an embodiment. Method 300 includes transferring 310 qubit population, where a 435-nm laser is used to transfer 315 qubit population in the |S 1 / 2 , F=0〉 state to the |D 3 / 2 , F=2〉 manifold of states. Transfer 315 is carried out via two consecutive laser pulses that are tuned to selectively populate the |D 3 / 2 , F=2,mF = ±2〉 hyperfine levels. The application of the second laser pulse increases the efficiency of transfer 315 approximately an order of magnitude, whereas a third pulse would not substantially increase the efficiency of transfer 315 beyond the use of two pulses.

[0012] Method 300 includes detecting 320 qubit bright or dark state, where three lasers are used to check if the qubit is in the bright or the dark state. First detection laser 325 includes a 369-nm laser connecting |S 1 / 2 , F=1〉 to |P 1 / 2 , F=0〉. Second detection laser 330 includes a 935-nm laser connecting |D 3 / 2 , F=1〉 to |[3 / 2] 1 / 2 , F=0〉. Third detection laser 335 includes a 369-nm laser connecting |S 1 / 2 , F=0〉 to |P 1 / 2 , F=1〉.

[0013] Method 300 includes returning 340 any 171Yb+ qubit in the D 3 / 2 state to the S 1 / 2 state. First return laser 345 includes a 935-nm laser connecting |D 3 / 2 , F=1〉 to |[3 / 2] 1 / 2 , F=0〉. Second return laser 350 includes a 935-nm laser connecting |D 3 / 2 , F=2〉 to |[3 / 2] 1 / 2 , F=1〉.

[0014] FIGs. 4A-4F are 171Yb+ states 400, according to an embodiment. 171Yb+ states 400 result from particular steps within method 300. FIG. 4A depicts transferring 310 qubit population, where the 435-nm laser is used to transfer 315 qubit population from the |S 1 / 2 , F=0〉 state to the |D 3 / 2 , F=2〉 manifold of states. Transfer 315 shown in FIG 4A is carried out via two consecutive laser pulses that are tuned to selectively populate the |D 3 / 2 , F=2,mF = ±2〉 hyperfine levels.

[0015] FIGs. 4B-4D show detecting 320 qubit bright or dark state. FIG. 4B shows first detection laser 325 that connects |S 1 / 2 , F=1〉 to |P 1 / 2 , F=0〉. FIG. 4C shows second detection laser 330 that connects |D 3 / 2 , F=1〉 to |[3 / 2] 1 / 2 , F=0〉. FIG. 4D shows third detection laser 335 that connects |S 1 / 2 , F=0〉 to |P 1 / 2 , F=1〉.

[0016] FIGs. 4E-4F show returning 340 any 171Yb+ qubit in the D 3 / 2 state to the S 1 / 2 state. FIG. 4E shows first return laser 345 connecting |D 3 / 2 , F=1〉 to |[3 / 2] 1 / 2 , F=0〉. FIG. 4F shows second return laser 350 connecting |D 3 / 2 , F=2〉 to |[3 / 2] 1 / 2 , F=1〉.

[0017] FIG. 5 is a block schematic diagram of a computer system 500 to implement ytterbium shelving detection, according to an example embodiment. The computer system 500 may utilize fewer components than shown in FIG. 5 in some embodiments to perform the methods described. One example computing device in the form of a computer 500, may include a processing unit 502, memory 503, removable storage 510, and non-removable storage 512. Memory 503 may include volatile memory 514 and non-volatile memory 508. Computer 500 may include - or have access to a computing environment that includes - a variety of computer-readable media, such as volatile memory 514 and non-volatile memory 508, removable storage 510 and non-removable storage 512. Computer storage includes random access memory (RAM), read only memory (ROM), erasable programmable read-only memory (EPROM) & electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD ROM), Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing computer-readable instructions. Computer 500 may include or have access to a computing environment that includes input 506, output 504, and a communication connection 516. The computer may operate in a networked environment using a communication connection to connect to one or more remote computers, such as database servers. The remote computer may include a personal computer (PC), server, router, network PC, a peer device or other common network node, or the like. The communication connection may include a Local Area Network (LAN), a Wide Area Network (WAN) or other networks.

[0018] Computer-readable instructions stored on a computer-readable medium are executable by the processing unit 502 of the computer 500. A hard drive, CD-ROM, and RAM are some examples of articles including a non-transitory computer-readable medium. For example, a computer program 518 capable of providing a generic technique to perform access control check for data access and / or for doing an operation on one of the servers in a component object model (COM) based system may be included on a CD-ROM and loaded from the CD-ROM to a hard drive. The computer-readable instructions allow computer 500 to provide generic access controls in a COM based computer network system having multiple users and servers.

[0019] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as "examples." Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided.

[0020] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In this document, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0021] The above description is intended to be illustrative, and not restrictive. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope should be determined with reference to the appended claims.

Claims

1. A quantum computing state detection system for detecting logical states of ytterbium-171 ion hyperfine qubits by detecting their bright or dark states, the system comprising: a shelving laser configured to apply two consecutive 435-nm laser pulses to transfer (315), out of the ytterbium-171 ion hyperfine qubits, the population of ytterbium-171 ion hyperfine qubits that are in a |S1 / 2, F=0〉 initial dark state (235) from the |S1 / 2, F=0〉 initial dark state (235) to a shelved dark state (260) |D3 / 2, F=2〉, in which the two consecutive 435-nm laser pulses are tuned to selectively populate hyperfine shelving levels |D3 / 2, F=2〉; three detection lasers (325, 330, 335) configured to apply three detection laser pulses to the ytterbium-171 ion hyperfine qubits to determine their bright or dark states, wherein the three detection lasers (325, 330, 335) comprise: a first detection laser (325) adapted to apply a 369-nm laser pulse connecting a |S1 / 2, F=1〉 state to a |P1 / 2, F=0〉 state; a second detection laser (330) adapted to apply a 935-nm laser pulse connecting a |D3 / 2, F=1〉 state to a |[3 / 2]1 / 2, F=0〉 state; and a third detection laser (335) adapted to apply a 369-nm laser pulse connecting a |S1 / 2, F=0〉 state to a |P1 / 2, F=1〉 state; the quantum computing state detection system being further configured to detect the bright or dark state of the ytterbium-171 ion hyperfine qubits in response to the application of the three detection laser pulses by collecting light from decay transitions (220, 225) from the |P1 / 2〉 states to the |S1 / 2, F=0〉 state and |S1 / 2, F=1〉 state, and the two consecutive 435-nm laser pulses being applied before collecting light from the decay transitions (220, 225); and the quantum computing state detection system further comprising two return lasers (345, 350) configured to return any ytterbium-171 ion hyperfine qubit in the |D3 / 2, F=1〉 state and |D3 / 2, F=2〉 state to the |S1 / 2, F=0〉 initial dark state, wherein the two return lasers (345, 350) comprise: a first return laser (345) adapted to apply a 935-nm laser connecting a |D3 / 2, F=1〉 to a |[3 / 2]1 / 2, F=0〉 state; and a second return laser (350) adapted to apply a 935-nm laser connecting a |D3 / 2, F=2〉 state to a |[3 / 2]1 / 2, F=1〉 state.

2. A quantum computing state detection method for detecting logical states of ytterbium-171 ion hyperfine qubits by detecting their bright of dark states, the method comprising: transferring (315), out of the ytterbium-171 ion hyperfine qubits, the population of ytterbium-171 ion hyperfine qubits that are in a |S1 / 2, F=0〉 initial dark state (235) from the |S1 / 2, F=0〉 initial dark state to a shelved dark state (260) |D3 / 2, F=2〉 by applying, by a shelving laser, two consecutive 435-nm laser pulses tuned to selectively populate hyperfine shelving levels |D3 / 2, F=2〉; detecting (325, 330, 335) bright or dark state of the ytterbium-171 ion hyperfine qubits in response to the application of three detection laser pulses to the ytterbium-171 ion hyperfine qubits by collecting light from decay transitions (220, 225) from the |P1 / 2〉 states to the |S1 / 2, F=0〉 state and |S1 / 2, F=1〉 state, the two consecutive 435-nm laser pulses being applied before collecting light from the decay transitions (220, 225), wherein applying the three detection laser pulses comprises: applying, by a first detection laser (325), a 369-nm laser pulse connecting a |S1 / 2, F=1〉 state to a |P1 / 2, F=0〉 state; applying, by a second detection laser (330), a 935-nm laser pulse connecting a |D3 / 2, F=1〉 state to a |[3 / 2] 1 / 2, F=0〉 state; applying, by a third detection laser (335), a 369-nm laser pulse connecting a |S1 / 2, F=0〉 state to a |P1 / 2, F=1〉 state; the method further comprising returning (345, 350) any ytterbium-171 ion hyperfine qubit in the |D3 / 2, F=1〉 state and |D3 / 2, F=2〉 state to the |S1 / 2, F=0〉 initial dark state by: applying, by a first return laser (345), a 935-nm laser connecting a |D3 / 2, F=1〉 to a |[3 / 2] 1 / 2, F=0〉 state; and applying, by a second return laser (350), a 935-nm laser connecting a |D3 / 2, F=2〉 state to a |[3 / 2] 1 / 2, F=1〉 state.

3. A machine-readable storage medium comprising a plurality of instructions that, when executed with a processor of a quantum computing state detection system, the quantum computing state detection system being according to claim 1, cause the quantum computing state detection system to carry out a method according to claim 2.