High-fidelity elementary operations for superconducting quantum computers

Eric Hyyppä

High-fidelity elementary operations for superconducting quantum computers

Julkaisun otsikon käännös: Tarkkojen alkeisoperaatioiden implementointi suprajohtavissa kvanttitietokoneissa

Eric Hyyppä

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Suprajohtavat kvanttipiirit tarjoavat yhden lupaavimmista lähestymistavoista tehokkaan kvanttitietokoneen toteuttamiseen, jolla saattaa tulevaisuudessa olla sovelluksia muun muassa kvanttikemian ja kryptografian aloilla. Kvanttietokoneen hyötyjen saavuttaminen edellyttää kuitenkin riittävän suurta määrää toisiinsa kytkettyjä kvanttibittejä eli kubitteja sekä kykyä suorittaa tarkkoja alkeisoperaatioita kubiteilla. Näihin alkeisoperaatioihin lukeutuvat muun muassa yhden ja kahden kubitin logiikkaportit sekä kubittien alustaminen tunnettuun tilaan. Nykyisissä transmon-kubitteihin perustuvissa suprajohtavissa kvanttietokoneissa alkeisoperaatiot ovat vielä liian virhealttiita hyödyllisen mittakaavan laskutoimitusten suorittamiseen riittävällä tarkkuudella. Alkeisoperaatioiden virheitä aiheuttavat muun muassa ympäristön kohinasta aiheutuva dekoherenssi sekä vuotovirheet laskenta-avaruuden ulkopuolisiin tiloihin. Tässä väitöskirjassa kehitetään uusia menetelmiä aiempaa tarkempien ja nopeampien alkeisoperaatioiden mahdollistamiseksi suprajohtavissa kvanttietokoneissa neljän eri lähestymistavan kautta. Ensiksi väitöskirjassa tutkitaan teoreettisesti ja kokeellisesti uutta suprajohtavaa unimon-kubittia, joka koostuu maadoitetusta gradiometrisesta värähtelijästä ja siihen sijoitetusta Josephsonin liitoksesta. Unimon-kubitissa yhdistyy monta hyödyllistä ominaisuutta, joita tarkkojen alkeisoperaatioiden toteuttaminen edellyttää, kuten suuri epälinearisuus transmon-kubittiin verrattuna sekä suoja haitallista matalantaajuuden varauskohinaa vastaan. Näiden ominaisuuksien ansiosta saavutimme lupaavan 99.9%:n tarkkuuden yhden kubitin logiikkaporteille jo ensimmäisillä valmistetuilla unimon-kubiteilla. Väitöskirjan toisessa osassa kehitetään uusia analyyttisiä menetelmiä vuotovirheiden vähentämiseksi nopeissa yhden kubitin porteissa. Kokeelliset mittauksemme transmon-kubitilla osoittavat, että uudet menetelmät alentavat vuotovirheiden todennäköisyyttä jopa 95%:lla verrattuna aiempiin johtaviin menetelmiin. Väitöskirjan kolmannessa osassa tutkitaan uudenlaista ratkaisua kubittien välisen muokattavan kytkennän toteuttamiseksi, joka kokeidemme perusteella mahdollistaa tarkat kahden kubitin CZ-logiikkaportit samalla tarjoten riittävästi tilaa kubittien nopeaan mittaukseen käytetyille rakenteille. Väitöskirjan viimeisessä osassa tarkastellaan kvanttipiirijäähdyttimen sovelluksia muun muassa suprajohtavien piirien alustamisessa ja vahvistinketjujen mittaamisessa. Väitöskirjassa kehitetyillä menetelmillä on potentiaalia parantaa alkeisoperaatioiden tarkkuutta ja suoritustaajuutta suuren kokoluokan suprajohtavissa kvanttietokoneissa. Osa työssä kehitetyistä menetelmistä, kuten analyyttiset pulssimuodot vuotovirheiden vähentämiseen, voivat olla hyödyllisiä suprajohtavien kubittien lisäksi myös muilla kubittialustoilla.

Julkaisun otsikon käännös	Tarkkojen alkeisoperaatioiden implementointi suprajohtavissa kvanttitietokoneissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Ohjaaja	Möttönen, Mikko, Vastuuprofessori Heinsoo, Johannes, Ohjaaja Tarasinski, Brian, Ohjaaja, Ulkoinen henkilö
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-2109-4
Sähköinen ISBN	978-952-64-2110-0
Tila	Julkaistu - 2024
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

suprajohtava kvanttipiiri
suprajohtava kubitti
kvanttioperaatio
yhden kubitin logiikkaportti
kahden kubitin logiikkaportti
vuotovirhe
kvanttipiirijäähdytin

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-2110-0

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Aalto-yliopisto
Laitteistot/tilat: Facility
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Repo, P. (Manager) & Rissanen, A. (Other)
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@phdthesis{6ce411ebd52e4245900eb6c41165d96b,

title = "High-fidelity elementary operations for superconducting quantum computers",

abstract = "Superconducting circuits provide one of the leading architectures for the realization of a large-scale quantum computer, with potential future applications, e.g., in quantum physics simulations, quantum chemistry, and cryptography. To provide an advantage over classical computers, a quantum computer must contain a sufficiently large register of quantum bits, i.e., qubits, while enabling accurate and fast elementary operations on the qubits, including qubit initialization, single- and two-qubit quantum logic gates, and readout of the qubit state. In current superconducting quantum computers based on transmon qubits, these elementary operations are still too error-prone to achieve a computational advantage in problems of practical relevance mainly due to decoherence arising from noise, leakage errors to non-computational states, control imperfections, and unwanted residual interactions. In this thesis, we study novel circuits and control techniques for improving the speed and fidelity of elementary operations in superconducting quantum computers, with the focus on single- and two-qubit logic gates, and the initialization of superconducting circuits. First, we theoretically propose and experimentally demonstrate a novel superconducting qubit coined the unimon that is based on a Josephson junction embedded in a gradiometric superconducting resonator. The unimon is protected against low-frequency charge noise by design, while enabling high anharmonicities of up to 750 MHz and fast single-qubit gates with a fidelity of 99.9\% in our first experimental devices. Second, we investigate novel analytical control methods for suppressing leakage errors in fast single-qubit gates suffering from frequency crowding. In experiments on a transmon qubit, we demonstrate a 20-fold reduction in the leakage error of 6.25-ns single-qubit gates in comparison with previous state-of-the-art techniques. Third, we realize a long-distance tunable coupler for a scalable transmon-based architecture that enables fast two-qubit CZ gates with a fidelity of 99.8\%, a low residual ZZ interaction, and sufficient space for individual Purcell filters needed for fast qubit readout. Finally, we study the use of voltage-biased normal-metal–insulator–superconductor (NIS) junctions as a tunable dissipative environment for superconducting circuits, which allows us to characterize partly cryogenic amplification chains, to study fast initialization of a superconducting resonator, and to observe a broadband Lamb shift in a superconducting resonator. In the future, the methods presented in this thesis may improve the speed and fidelity of elementary operations in superconducting quantum processors, thus bringing the realization of useful quantum computers one step closer. Some of the proposed techniques, such as the analytical control pulses for fast logic gates, are essentially agnostic of the qubit type, and may even find applications in other quantum computing architectures.",

keywords = "superconducting quantum circuit, superconducting qubit, quantum operation, single-qubit gate, two-qubit gate, leakage error, quantum-circuit refrigerator, suprajohtava kvanttipiiri, suprajohtava kubitti, kvanttioperaatio, yhden kubitin logiikkaportti, kahden kubitin logiikkaportti, vuotovirhe, kvanttipiirij{\"a}{\"a}hdytin, superconducting quantum circuit, superconducting qubit, quantum operation, single-qubit gate, two-qubit gate, leakage error, quantum-circuit refrigerator",

author = "Eric Hyypp{\"a}",

year = "2024",

language = "English",

isbn = "978-952-64-2109-4",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "235",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - High-fidelity elementary operations for superconducting quantum computers

AU - Hyyppä, Eric

PY - 2024

Y1 - 2024

N2 - Superconducting circuits provide one of the leading architectures for the realization of a large-scale quantum computer, with potential future applications, e.g., in quantum physics simulations, quantum chemistry, and cryptography. To provide an advantage over classical computers, a quantum computer must contain a sufficiently large register of quantum bits, i.e., qubits, while enabling accurate and fast elementary operations on the qubits, including qubit initialization, single- and two-qubit quantum logic gates, and readout of the qubit state. In current superconducting quantum computers based on transmon qubits, these elementary operations are still too error-prone to achieve a computational advantage in problems of practical relevance mainly due to decoherence arising from noise, leakage errors to non-computational states, control imperfections, and unwanted residual interactions. In this thesis, we study novel circuits and control techniques for improving the speed and fidelity of elementary operations in superconducting quantum computers, with the focus on single- and two-qubit logic gates, and the initialization of superconducting circuits. First, we theoretically propose and experimentally demonstrate a novel superconducting qubit coined the unimon that is based on a Josephson junction embedded in a gradiometric superconducting resonator. The unimon is protected against low-frequency charge noise by design, while enabling high anharmonicities of up to 750 MHz and fast single-qubit gates with a fidelity of 99.9% in our first experimental devices. Second, we investigate novel analytical control methods for suppressing leakage errors in fast single-qubit gates suffering from frequency crowding. In experiments on a transmon qubit, we demonstrate a 20-fold reduction in the leakage error of 6.25-ns single-qubit gates in comparison with previous state-of-the-art techniques. Third, we realize a long-distance tunable coupler for a scalable transmon-based architecture that enables fast two-qubit CZ gates with a fidelity of 99.8%, a low residual ZZ interaction, and sufficient space for individual Purcell filters needed for fast qubit readout. Finally, we study the use of voltage-biased normal-metal–insulator–superconductor (NIS) junctions as a tunable dissipative environment for superconducting circuits, which allows us to characterize partly cryogenic amplification chains, to study fast initialization of a superconducting resonator, and to observe a broadband Lamb shift in a superconducting resonator. In the future, the methods presented in this thesis may improve the speed and fidelity of elementary operations in superconducting quantum processors, thus bringing the realization of useful quantum computers one step closer. Some of the proposed techniques, such as the analytical control pulses for fast logic gates, are essentially agnostic of the qubit type, and may even find applications in other quantum computing architectures.

AB - Superconducting circuits provide one of the leading architectures for the realization of a large-scale quantum computer, with potential future applications, e.g., in quantum physics simulations, quantum chemistry, and cryptography. To provide an advantage over classical computers, a quantum computer must contain a sufficiently large register of quantum bits, i.e., qubits, while enabling accurate and fast elementary operations on the qubits, including qubit initialization, single- and two-qubit quantum logic gates, and readout of the qubit state. In current superconducting quantum computers based on transmon qubits, these elementary operations are still too error-prone to achieve a computational advantage in problems of practical relevance mainly due to decoherence arising from noise, leakage errors to non-computational states, control imperfections, and unwanted residual interactions. In this thesis, we study novel circuits and control techniques for improving the speed and fidelity of elementary operations in superconducting quantum computers, with the focus on single- and two-qubit logic gates, and the initialization of superconducting circuits. First, we theoretically propose and experimentally demonstrate a novel superconducting qubit coined the unimon that is based on a Josephson junction embedded in a gradiometric superconducting resonator. The unimon is protected against low-frequency charge noise by design, while enabling high anharmonicities of up to 750 MHz and fast single-qubit gates with a fidelity of 99.9% in our first experimental devices. Second, we investigate novel analytical control methods for suppressing leakage errors in fast single-qubit gates suffering from frequency crowding. In experiments on a transmon qubit, we demonstrate a 20-fold reduction in the leakage error of 6.25-ns single-qubit gates in comparison with previous state-of-the-art techniques. Third, we realize a long-distance tunable coupler for a scalable transmon-based architecture that enables fast two-qubit CZ gates with a fidelity of 99.8%, a low residual ZZ interaction, and sufficient space for individual Purcell filters needed for fast qubit readout. Finally, we study the use of voltage-biased normal-metal–insulator–superconductor (NIS) junctions as a tunable dissipative environment for superconducting circuits, which allows us to characterize partly cryogenic amplification chains, to study fast initialization of a superconducting resonator, and to observe a broadband Lamb shift in a superconducting resonator. In the future, the methods presented in this thesis may improve the speed and fidelity of elementary operations in superconducting quantum processors, thus bringing the realization of useful quantum computers one step closer. Some of the proposed techniques, such as the analytical control pulses for fast logic gates, are essentially agnostic of the qubit type, and may even find applications in other quantum computing architectures.

KW - superconducting quantum circuit

KW - superconducting qubit

KW - quantum operation

KW - single-qubit gate

KW - two-qubit gate

KW - leakage error

KW - quantum-circuit refrigerator

KW - suprajohtava kvanttipiiri

KW - suprajohtava kubitti

KW - kvanttioperaatio

KW - yhden kubitin logiikkaportti

KW - kahden kubitin logiikkaportti

KW - vuotovirhe

KW - kvanttipiirijäähdytin

KW - superconducting quantum circuit

KW - superconducting qubit

KW - quantum operation

KW - single-qubit gate

KW - two-qubit gate

KW - leakage error

KW - quantum-circuit refrigerator

M3 - Doctoral Thesis

SN - 978-952-64-2109-4

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

High-fidelity elementary operations for superconducting quantum computers

Abstrakti

Tutkimusalat

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