US-12619899-B2 - Laser on-demand scrambling of two-level systems in superconducting qubits

Abstract

Methods and systems for mitigating the effects of defects in a quantum processor are provided. A mitigation system uses an iterative process of applying light pulses and examining qubit relaxation times to eliminate or minimize two-level system (TLS) interaction with qubits. The system applies a first light pulse to illuminate a quantum processor having one or more qubits. The system receives qubit relaxation times that are measured at different electric field frequencies after applying the first light pulse. The system applies a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled TLS in the quantum processor.

Inventors

• Abram L. Falk
• Martin O. Sandberg
• Karthik Balakrishnan
• Oliver Dial
• Jason S. Orcutt

Assignees

• INTERNATIONAL BUSINESS MACHINES CORPORATION

Dates

Publication Date

20260505

Application Date

20221013

Claims (20)

1. 1 . A method comprising: applying a first light pulse to illuminate a quantum processor comprising one or more qubits; receiving qubit relaxation times that are measured at different qubit frequencies after applying the first light pulse; and applying a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled two-level system (TLS) in the quantum processor, wherein the presence of strongly coupled TLS in the quantum processor is indicated by a received qubit relaxation time being less than a threshold ratio of an expected qubit relaxation time at a frequency of interest.
2. 2 . The method of claim 1 , wherein at least one of the first or second the light pulses scrambles a frequency landscape of the TLSs, the frequency landscape comprising the received qubit relaxation times measured at different qubit frequencies.
3. 3 . The method of claim 1 , wherein the threshold ratio is 0.75.
4. 4 . The method of claim 1 , further comprising receiving performance parameters of one or more qubits in the quantum processor to identify a qubit that fails to meet a performance threshold, wherein the received qubit relaxation times comprises relaxation times of the identified qubit.
5. 5 . The method of claim 4 , wherein the first and second light pulses are local to the identified qubit.
6. 6 . The method of claim 1 , wherein the first and second light pulses are global to the quantum processor and illuminate multiple qubits in the quantum processor.
7. 7 . A computer program product comprising: one or more non-transitory computer-readable storage devices and program instructions stored on at least one of the one or more non-transitory storage devices, the program instructions executable by a processor, the program instructions comprising sets of instructions for: applying a first light pulse to illuminate a quantum processor comprising one or more qubits; receiving qubit relaxation times that are measured at different qubit frequencies after applying the first light pulse; and applying a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled two-level system (TLS) in the quantum processor, wherein the presence of strongly coupled TLS in the quantum processor is indicated by a received qubit relaxation time being less than a threshold ratio of an expected qubit relaxation time at a frequency of interest.
8. 8 . The computer program product of claim 7 , wherein at least one of the first or second light pulses is used to scramble a frequency landscape of the TLSs, the frequency landscape comprising the received qubit relaxation times measured at different qubit frequencies.
9. 9 . The computer program product of claim 7 , wherein the threshold ratio is 0.75.
10. 10 . The computer program product of claim 7 , wherein the sets of instructions further comprise receiving performance parameters of one or more qubits in the quantum processor to identify a qubit that fails to meet a performance threshold, wherein the received qubit relaxation times comprises relaxation times of the identified qubit.
11. 11 . The computer program product of claim 10 , wherein the first and second light pulses are local to the identified qubit and illuminate only the identified qubit and no other qubit.
12. 12 . The computer program product of claim 7 , wherein the first and second light pulses are global to the quantum processor and illuminate multiple qubits in the quantum processor.
13. 13 . A system comprising: a quantum processor comprising one or more qubits; a two-level system (TLS) mitigation controller configured to perform acts comprising: applying a first light pulse to illuminate a quantum processor comprising one or more qubits; receiving qubit relaxation times that are measured at different qubit frequencies after applying the first light pulse; and applying a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled TLS in the quantum processor, wherein the presence of strongly coupled TLS in the quantum processor is indicated by a received qubit relaxation time being less than a threshold ratio of an expected qubit relaxation time at a frequency of interest.
14. 14 . The system of claim 13 , wherein at least one of the first or second the light pulses is used to scramble a frequency landscape of the TLS in the quantum processor, the frequency landscape comprising the received qubit relaxation times measured at different qubit frequencies.
15. 15 . The system of claim 13 , wherein the threshold ratio is 0.75.
16. 16 . The system of claim 13 , wherein the acts further comprise receiving performance parameters of one or more qubits in the quantum processor to identify a qubit that fails to meet a performance threshold, wherein the received qubit relaxation times comprises relaxation times of the identified qubit.
17. 17 . The system of claim 16 , wherein the first and second light pulses is local to the identified qubit and illuminate only the identified qubit and no other qubit.
18. 18 . The system of claim 13 , wherein the first and second light pulses are global to the quantum processor and illuminate multiple qubits in the quantum processor.
19. 19 . A method comprising: providing a quantum processor comprising one or more qubits; configuring a two-level system (TLS) mitigation controller to perform acts comprising: applying a first light pulse to illuminate a quantum processor comprising one or more qubits; receiving qubit relaxation times that are measured at different electric field frequencies after applying the first light pulse; and applying a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled TLS in the quantum processor wherein the presence of strongly coupled TLS in the quantum processor is indicated by a received qubit relaxation time being less than a threshold ratio of an expected qubit relaxation time at a frequency of interest.
20. 20 . The method of claim 19 , wherein the threshold ratio is 0.75.

Description

BACKGROUND Technical Field The present disclosure generally relates to quantum computing, and more particularly, to laser on-demand scrambling of superconducting qubits. Description of the Related Arts A quantum bit, or qubit, is the basic element for information encoding in a quantum computer. A two-level system, or TLS, is a spurious quantum system that can couple to a qubit and cause decoherence. TLSs are one of the main sources of decoherence in superconducting quantum circuits. Typically, the TLSs include of two sets: a large set of low frequency two level fluctuators (a bath) and a few discrete two-level systems that are near resonant with the qubit transition. If a TLS strongly interacts with a qubit, the qubit becomes inoperable due to frequency shifts and decoherence. The nature of these TLSs is not fully understood but are believed to originate from crystal defects, surface defects, or atomic level defects in the materials that generate microscopic dipoles (atomic or electron traps) that interact with a qubit (e.g., couple to the electric fields of the qubit). The TLSs are always present and randomly distributed. Two-level systems can be either off-resonant or on-resonant with the qubit. On-resonant TLSs are much more detrimental than off-resonant TLSs. These on-resonant, strongly coupled TLS, have a significant detrimental effect on gate fidelities in the processor. This is true for processors based on fixed frequency qubits and for processors based on flux tunable qubits. SUMMARY Some embodiments of the disclosure provide methods and systems for mitigating the effects of defects in a quantum processor are presented. In some embodiments, a mitigation system uses an iterative process of applying light pulses and examining qubit relaxation times to eliminate or minimize two-level system (TLS) interaction with qubits. The system applies a first light pulse to illuminate a quantum processor having one or more qubits. The light pulse is used to scramble the ensemble of TLSs coupled to the quantum processor. The system is characterized by qubit relaxation times that are measured at different qubit frequencies after applying the first light pulse. The system applies a second light pulse to illuminate the quantum processor upon determining that the received qubit relaxation times indicates presence of a strongly coupled TLS in the quantum processor. In some embodiments, the system may determine whether to apply a second light pulse based on a TLS configuration of the quantum processor that is determined from the received qubit relaxation times at different qubit frequencies. The system may determine whether to apply the second light pulse based on whether a TLS is interacting with a qubit based on the TLS configuration. Following that, a third light pulse may be applied, and subsequent light pulses after that. Light pulses will continue to be applied until the quantum processor is characterized by acceptable TLS configurations. In some embodiments, the system receives performance parameters (e.g., coherence properties) of one or more qubits in the quantum processor to identify a qubit that fails to meet a performance threshold. The received qubit relaxation times includes relaxation times of the identified qubit. In an embodiment that can be combined with previous embodiments, the first and second light pulses is local to the identified qubit and illuminate only the identified qubit and no other qubit. In some embodiments, the first and second light pulses is global to the quantum processor and illuminate multiple qubits in the quantum processor. Two-level systems are one of the most fundamental problems in superconducting qubits, as they are the dominant source of decoherence. The capability to focus light on specific qubits may improve the coherence of qubits quickly, rather than relying on time-consuming processes such as heating the entire quantum processor. The preceding Summary is intended to serve as a brief introduction to some embodiments of the disclosure. It is not meant to be an introduction or overview of all inventive subject matter disclosed in this document. The Detailed Description that follows and the Drawings that are referred to in the Detailed Description will further describe the embodiments described in the Summary as well as other embodiments. Accordingly, to understand all the embodiments described by this document, a Summary, Detailed Description and the Drawings are provided. Moreover, the claimed subject matter is not to be limited by the illustrative details in the Summary, Detailed Description, and the Drawings, but rather is to be defined by the appended claims, because the claimed subject matter can be embodied in other specific forms without departing from the spirit of the subject matter. BRIEF DESCRIPTION OF THE DRAWINGS The drawings are of illustrative embodiments. They do not illustrate all embodiments. Other embodiments may be used in addition or instead. Details tha