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Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences
Chalmers Univ Technol, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
Chalmers Univ Technol, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
Chalmers Univ Technol, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
Chalmers Univ Technol, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
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2022 (English)In: PRX QUANTUM, ISSN 2691-3399, Vol. 3, no 3, article id 030301Article in journal (Refereed) Published
Abstract [en]

Hosting nonclassical states of light in three-dimensional microwave cavities has emerged as a promising paradigm for continuous-variable quantum information processing. Here we experimentally demonstrate high-fidelity generation of a range of Wigner-negative states useful for quantum computation, such as Schrodinger-cat states, binomial states, Gottesman-Kitaev-Preskill states, as well as cubic phase states. The latter states have been long sought after in quantum optics and have never been achieved experimentally before. We use a sequence of interleaved selective number-dependent arbitrary phase (SNAP) gates and displacements. We optimize the state preparation in two steps. First we use a gradient-descent algorithm to optimize the parameters of the SNAP and displacement gates. Then we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly nonclassical states in a harmonic oscillator is robust to fluctuations of the system parameters such as the qubit frequency and the dispersive shift.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2022. Vol. 3, no 3, article id 030301
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-315915DOI: 10.1103/PRXQuantum.3.030301ISI: 000823762500001Scopus ID: 2-s2.0-85136004195OAI: oai:DiVA.org:kth-315915DiVA, id: diva2:1684753
Note

QC 20220728

Available from: 2022-07-28 Created: 2022-07-28 Last updated: 2023-12-22Bibliographically approved
In thesis
1. Digital measurement and control of microwave quantum circuits
Open this publication in new window or tab >>Digital measurement and control of microwave quantum circuits
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Superconducting circuits are well established tools for quantum sensing anda promising new platform for quantum computing. Typically these quantumcircuits operate at microwave frequencies where the thermal noise at 10mK in a dilution refrigerator is small compared to the ground-state energy.Controlling the quantum state of these circuits requires well-timed, phase-coherent microwave pulses. This thesis describes an instrument based onsynchronous direct digital synthesis and sampling at microwave frequenciesto control and measure the response of superconducting quantum circuits.This all-digital approach allows for up and down conversion to microwavebands without analog IQ mixers, reducing the complexity of the controlsystem and enabling advanced signal processing via software. The thesisalso describes how the instrument is used to explore the quantum propertiesof a variety of different superconducting circuits.We characterise and benchmark a sample containing two transmon qubitsconnected by a parametric coupler. Randomized benchmarking showscoherence-limited fidelity of single-qubit gates. We successfully operate atwo-qubit iSWAP gate where controlling the relative phase of microwavepulses is necessary. Using a 3D cavity coupled to a transmon qubit we createarbitrary bosonic states using interleaved sequences of pulses which displacethe cavity oscillation and perform selective number-dependent arbitrary-phase (SNAP) gates. In the area of measurement-based quantum computingwe explore the generation of entangled states of travelling waves generatedby scattering vacuum noise off a Josephson parametric amplifier. The en-tanglement is generated and detected using a phase-coherent pumping anddetection scheme at multiple frequencies. We apply this same scheme to alsostudy frequency-domain entanglement between multiple standing waves ofa nonlinear surface-acoustic-wave resonator. The multifrequency capabili-ties of the instrument are also used to study single-photon detection in thefar infrared by multiplexed readout of arrays of quantum-capacitance sen-sors. The capabilities of the instrument are further showcased through theimplementation of a coherent real-time noise-radar system, highlighting itspractical utility beyond quantum exploration.

Abstract [sv]

Supraledande kretsar är väletablerade för kvantsensorer och en lovande nyplattform för kvantdatorer. Kretsarna är normalt designade för att använ-das vid mikrovågsfrekvenser där det termiska bruset vid 10 mK i en kryostatär litet jämfört med grundtillståndens energi. Att kontrollera kvanttillståndi sådana kretsar kräver vältajmade, faskoherenta mikrovågspulser. Dennaavhandling beskriver ett instrument baserat på synkroniserad direkt digi-tal syntes och sampling vid mikrovågsfrekvenser avsett att kontrollera ochmäta svar från supraledande kvantkretsar. Detta helt digitala tillvägagångs-sätt tillåter upp- och nedkonvertering till mikrovågsfrekvenser utan analogaIQ-mixers vilket minskar instrumentets komplexitet och möjliggör avance-rad signalbehandling i mjukvara. Avhandlingen beskriver också hur instru-mentet används till att utforska kvantegenskaperna hos olika supraledandekretsar.Vi karakteriserar och utvärderar prestanda på ett prov innehållande tvåkvantbitar av typen ’transmon’ sammankopplade med en parametrisk kopp-lare. ’Randomized benchmarking’ visar att noggrannheten på en-kvantbitgrindar är begränsade av kvantbitens koherenstid. Vi lyckas framgångsriktgenomföra en iSWAP-grind där styrning av den relativa fasen på mikrovågs-pulser är nödvändig. Med hjälp av en 3D-kavitet kopplad till en ’transmon’kvantbit skapar vi godtyckliga bosoniska tillstånd via sammanflätade se-kvenser av pulser som förskjuter kavitetsoscillationen och selective number-dependent arbitrary phase (SNAP) grindar. I kategorin mätningabasera-de kvantberäkningar utforskar vi generering av sammanflätade tillstånd iform av vågor som skapas genom att låta vakuumbrus reflekteras på enJosephson-parametrisk förstärkare. Sammanflätningen genereras och detek-teras via faskoherent pump- och detektion på flera frekvenser. Vi tillämparsamma metod för att studera sammanflätning mellan stående vågor i en icke-linjär akustisk ytvågresonator. Instrumentets multifrekvensfunktioner an-vänds också till att studera singelfotondetektion i fjärrinfrarött ljus via mul-tiplexad avläsning av kvantkapacitanssensorer. Instrumentets möjligheterdemonstreras vidare genom att implementera ett realtids-brusradarsystem,som visar att det är praktiskt användbart även utanför kvantforskning.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. p. 77
Series
TRITA-SCI-FOU ; 2023:66
Keywords
Superconducting circuits, circuit QED, quantum sensing, quantum capaci- tance, 3D cavity, bosonic codes, noise radar, instrumentation, supraledande kretsar, krets QED, kvantavkänning, kvantkapacitans, 3D ka- vitet, bosonic codes, brusradar, mätinstrument
National Category
Condensed Matter Physics
Research subject
Physics, Material and Nano Physics
Identifiers
urn:nbn:se:kth:diva-341578 (URN)978-91-8040-810-3 (ISBN)
Public defence
2024-01-31, FA32 Albanova, Roslagstullsbacken 21, Stockholm, 09:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 2023-12-22

Available from: 2023-12-22 Created: 2023-12-22 Last updated: 2024-01-03Bibliographically approved

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Tholen, Mats O.Borgani, RiccardoHaviland, David B.

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