This document develops a theoretical, technical, and experimental framework for activethermal compensation of quantum-control pulses in superconducting qubits. The centralproposal is to measure a temperature-related control variable and use that information toadapt the microwave control amplitude so that the realized gate rotation is less sensitive toslow or reproducible thermal variations.Version 2.0 makes an important distinction between established physical relations andphenomenological assumptions. In particular, no universal linear dependence of the Rabifrequency on temperature is assumed. Instead, the temperature-to-control response is rep-resented by experimentally identifiable transfer functions and local calibration coefficients.Possible microscopic contributions from quasiparticles, thermal photons, two-level systems,dielectric loss, and other environmental channels are treated as candidate mechanisms ratherthan as a universal additive law.The control problem is formulated using a driven two-level Hamiltonian with both am-plitude and detuning errors. A thermal sensitivity coefficient is introduced through theexperimentally measurable derivative of the effective Rabi frequency with respect to tem-perature. The compensation law is derived from this measured response. Finite sensor andactuator bandwidth are incorporated through a causal filter and an explicit latency term.The experimental protocol combines Rabi calibration, thermal characterization, random-ized benchmarking, interleaved randomized benchmarking, and independent measurementsof T1 and T∗2. The primary experimental question is whether active thermal compensationproduces a statistically and experimentally resolvable reduction of gate error under controlledthermal perturbations.The proposal does not assume a predetermined improvement in fidelity, and it does notassume that amplitude compensation automatically suppresses all thermal decoherence. Allnumerical coefficients introduced in this document are design parameters or initial experi-mental ranges unless explicitly identified as measured quantities. No experimental result isclaimed.
This document develops a theoretical, technical, and experimental framework for activethermal compensation of quantum-control pulses in superconducting qubits. The centralproposal is to measure a temperature-related control variable and use that information toadapt the microwave control amplitude so that the realized gate rotation is less sensitive toslow or reproducible thermal variations.Version 2.0 makes an important distinction between established physical relations andphenomenological assumptions. In particular, no universal linear dependence of the Rabifrequency on temperature is assumed. Instead, the temperature-to-control response is rep-resented by experimentally identifiable transfer functions and local calibration coefficients.Possible microscopic contributions from quasiparticles, thermal photons, two-level systems,dielectric loss, and other environmental channels are treated as candidate mechanisms ratherthan as a universal additive law.The control problem is formulated using a driven two-level Hamiltonian with both am-plitude and detuning errors. A thermal sensitivity coefficient is introduced through theexperimentally measurable derivative of the effective Rabi frequency with respect to tem-perature. The compensation law is derived from this measured response. Finite sensor andactuator bandwidth are incorporated through a causal filter and an explicit latency term.The experimental protocol combines Rabi calibration, thermal characterization, random-ized benchmarking, interleaved randomized benchmarking, and independent measurementsof T1 and T∗2. The primary experimental question is whether active thermal compensationproduces a statistically and experimentally resolvable reduction of gate error under controlledthermal perturbations.The proposal does not assume a predetermined improvement in fidelity, and it does notassume that amplitude compensation automatically suppresses all thermal decoherence. Allnumerical coefficients introduced in this document are design parameters or initial experi-mental ranges unless explicitly identified as measured quantities. No experimental result isclaimed.
This version develops a rigorous experimental framework for spatial thermal diagnosticsusing superconducting qubits as distributed sensing elements. The central methodologicalchange relative to a simple frequency-to-temperature conversion is the introduction of anexplicit measurement model separating thermal and non-thermal contributions to the observedqubit-frequency shift.For sensor i,δωobsi = δωthi + δωfluxi + δωqpi + δωTLSi + δωroi + δωotheri.Only after characterization of these contributions is a temperature estimate formed. Thelocal thermal response is represented by a calibrated coefficientαi(T0) = ∂ωq,i∂T⃓⃓⃓⃓T0,with explicit uncertainty and possible nonlinear correction.The spatial inverse problem is formulated through a response matrix, a point-spreadfunction (PSF), and regularized reconstruction. Spatial resolution is therefore not identifiedsimply with sensor spacing.The protocol introduces independent reference thermometry, blocked test data, blind lo-calized thermal perturbations, cross-validation, uncertainty propagation, hierarchical analysisacross cooldowns, and predefined falsification criteria. The primary endpoint is the inde-pendently evaluated reconstruction error of the thermal field. Secondary endpoints includeeffective spatial resolution, temperature resolution, localized perturbation detection, calibrationstability, and cross-cooldown reproducibility.The proposal remains exploratory and falsifiable. It does not claim experimental validation,universal thermometry, or superiority over conventional thermal sensors.
This work presents a theoretical, engineering, and experimental framework for a multi-stagecryogenic architecture with programmable thermal conductance. The objective is to inves-tigate whether dynamically controlled thermal links can modify the low-frequency thermalenvironment experienced by a superconducting quantum device without introducing compen-sating noise or instability.The architecture is represented as a lumped thermal network containing nodes with heat ca-pacities, thermal conductances, external heat loads, and stochastic heat-current sources. Thisformulation replaces a single-stage temperature-noise expression with a matrix description ofthermal fluctuations and transfer functions. For a linear network, the temperature fluctuationspectrum is obtained from the thermal susceptibility matrix and the spectral-density matrixof the dissipative heat-current sources.A central methodological distinction is made between (i) mean temperature, (ii) tempera-ture fluctuations, (iii) electromagnetic noise, (iv) mechanical/vibrational noise, and (v) qubitdecoherence. These quantities are not assumed to be equivalent.The programmable element is modeled as a controllable thermal conductance Gi(u, t).Its effect is evaluated together with the noise associated with the control mechanism, pos-sible electromagnetic coupling, mechanical coupling, and transient thermal response. Theexperimental protocol therefore contains matched passive and programmable conditions, ran-domized measurement order, independent calibration, thermal settling criteria, control-bandmeasurements, and reproducibility across cooldowns.The primary endpoint is a pre-registered, band-limited reduction in the temperature-noisepower spectral density at the quantum device stage. Secondary endpoints include integratedtemperature variance, qubit T1, qubit T∗2, and randomized-benchmarking metrics. The pro-posal does not assume that any secondary endpoint must improve.The framework is explicitly falsifiable. A programmable architecture can fail to provide anet benefit if it produces additional noise, thermal gradients, control instability, electromag-netic interference, mechanical coupling, excessive settling time, or no reproducible reductionin the predefined thermal-noise metric.
This work proposes an experimentally falsifiable framework for incorporating real-timethermal information into quantum error correction for superconducting qubits. The centralidea is not to assume a universal thermal error law, but to determine experimentally whetherlocal temperature, thermal gradients, and related thermal observables contain predictive in-formation about physical error probabilities.Version 3.1 replaces the previous additive phenomenological error expression with a boundedstatistical model based on conditional error probabilities. For each physical error channel a,the model has the generic formp(a)i(t) = logit−1[︂β(a)0 + β(a)TδTi(t) + β(a)∇T Gi(t) + β(a)τδτ (t) + β(a)·xi(t)]︂,where Gi represents a normalized local temperature-gradient observable and xi containsoptional control variables. A physically motivated thermal occupation term may be includedas a covariate, but it is not imposed as the complete error model.Three operating modes are compared:1. Mode A: fixed-rate baseline decoder;2. Mode B: thermal-information-aware decoder with fixed cycle duration;3. Mode C: thermal-information-aware decoder with bounded adaptive cycle duration.The primary endpoint is the logical error-rate ratio between Mode B and Mode A undermatched experimental conditions. The secondary endpoint compares Mode C with Mode B.The protocol incorporates calibration, cross-validation, pre-registration of the primaryendpoint, paired experimental blocks, bootstrap confidence intervals, multiple-comparisoncontrol, systematic-error analysis, placebo tests, latency characterization, and independentcooldown reproducibility.No experimental result is claimed.
Quantum control experiments are often subject to coherent, time-dependent disturbances that vary over timescales comparable to the experiment duration. We show that when such disturbances are reproducible with respect to a trigger signal, their effect can be measured and compensated through software-defined updates to the control frequency and phase. We experimentally verify the performance of our protocol using a trapped 137Ba+ ion experiencing magnetic-field-induced energy shifts synchronous with the laboratory AC mains power. Using this compensation technique, the calibrated AC line contribution to the instantaneous oscillator detuning is reduced by 21(9)×, and the fitted AC-induced phase amplitude is reduced below the measurement uncertainty. We use randomized benchmarking to validate the compensation performance in quantum gate sequences, recovering an average single-qubit gate fidelity of 99.93(1)\% with a magnetic-field-sensitive qubit. Finally, we extend the compensation framework to multi-level qudit control. Using the Bernstein-Vazirani algorithm as a benchmark, we increase the algorithm's success probability from 10(7)\% to 70(9)\% in a 16 level system when compensation is enabled. Our results demonstrate that trigger-synchronized coherent errors can be reframed as deterministic control-frame errors and corrected in software.
In the last decade, quantum information processing has transformed from a field of mostly academic research to an applied engineering subfield with many commercial companies announcing strategies to achieve quantum advantage and construct a useful universal quantum computer. Continuing efforts to improve qubit lifetime, control techniques, materials and fabrication methods together with exploring ways to scale up the architecture have culminated in the recent achievement of quantum supremacy using a programmable superconducting processor -- a major milestone in quantum computing en route to useful devices. Marking the point when for the first time a quantum processor can outperform the best classical supercomputer, it heralds a new era in computer science, technology and information processing.One of the key developments enabling this transition to happen is the ability to exert more precise control over quantum bits and the ability to detect and mitigate control errors and imperfections. In this thesis, ways to efficiently control superconducting qubits are explored from the experimental viewpoint.We introduce a state-of-the-art experimental machinery enabling one to perform one- and two-qubit gates focusing on the technical aspect and outlining some guidelines for its efficient operation. We describe the software stack from the time alignment of control pulses and triggers to the data processing organisation. We then bring in the standard qubit manipulation and readout methods and proceed to describe some of the more advanced optimal control and calibration techniques.The described toolbox together with some newly developed advances such as multi-level single-shot readout are applied to a practical problem of generating high-quality random numbers. Following the recent advances in the field, we certify our generator based on the Kochen-Specker theorem utilizing contextuality of quantum mechanics as an underlying resource of randomness. Our implementation based on the solid-state circuit quantum electrodynamics (QED) platform and the new certification scheme allows us to greatly enhance the bit rate of certified quantum random number generators (QRNGs) and approach the requirements for real-world applications.Addressing some of the control and state preparation errors, we develop a set of techniques to use a qubit as an in situ probe of distortions of its control lines and its effective temperature. Considering a qubit simultaneously driven by a longitudinal and a transverse MW-drives under certain resonant conditions, we show that in the rotating dressed-state picture (second rotating frame) one can get information about both the amplitude and the phase of the drive signals. This allows us to employ a qubit as an on-chip vector network analyzer and precisely measure the transfer functions of its control lines. As no other method with comparable frequency domain coverage exists, we verify our technique by cancelling out the distortions and increasing the fidelity of entangling two-qubit CPHASE gate.Finally, we show that the decay of the correlations between two sequential measurements of a quantum bit is a manifestation of its nonzero effective temperature. We use it to develop a precise method of evaluating the qubits population allowing for virtually unlimited suppression of absolute errors. We realize the method and demonstrate its applicability to the calibration of a quantum processor and evaluation of active reset techniques. As the actual mechanism of the increased excited-state population is currently unknown, we use our method's precision to show the qubit’s coupling to two separate independent thermal baths. We also introduce the ‘temperature spectroscopy’ as a tool to acquire more information about the qubits spurious excitation sources.
This thesis discusses a series of experimental and theoretical studies on fast control and decoherence in superconducting quantum circuits. These two subjects are complementary aspects of the problem of improving the gate fidelities in quantum information processing devices based on superconducting circuits. \n \nIn the first part of this thesis, we present experiments on fast control of a superconducting flux qubit using strong driving. We explore driving with short pulses and a driving strength significantly exceeding the transition frequency. The observed dynamics is described in terms of quasienergies and quasienergy states, in agreement with Floquet theory. We observe the role of pulse shaping in the dynamics, as determined by non-adiabatic transitions between Floquet states. In addition, based on adiabatic perturbation theory in the Floquet picture, we propose a control scheme for fast and high-fidelity single-qubit operations with strong driving. These results pave the way to quantum control with a fidelity beyond the threshold of fault-tolerant quantum computation. \n \nIn the second part of this thesis, we discuss experimental methods and present the characterization of decoherence in superconducting resonators and superconducting qubits. Firstly, we present an analysis method on the measurements of photon loss in superconducting resonators. We use this method to characterize the microwave loss of aluminum oxide, an important material in superconducting circuits. The power and temperature dependence of the measured loss is consistent with loss due to two-level defects in amorphous materials. Secondly, we present experimental results on decoherence and noise spectroscopy of a superconducting flux qubit. Using the qubit as a noise spectrometer, we perform detailed measurements on the power spectral density of the flux noise in superconducting circuits over a wide range of frequencies, from 10^-3 to 10^8 Hz, and over a temperature range from 35 to 130 mK. We also present measurements of frequency and temperature dependence of the qubit energy relaxation.