Journal articles: 'Radio-Frequency superconducting qubit'

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Tholén, Mats O., Riccardo Borgani, Giuseppe Ruggero Di Carlo, Andreas Bengtsson, Christian Križan, Marina Kudra, Giovanna Tancredi, et al. "Measurement and control of a superconducting quantum processor with a fully integrated radio-frequency system on a chip." Review of Scientific Instruments 93, no. 10 (October 1, 2022): 104711. http://dx.doi.org/10.1063/5.0101398.

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We describe a digital microwave platform called Presto, designed for measurement and control of multiple quantum bits (qubits) and based on the third-generation radio-frequency system on a chip. Presto uses direct digital synthesis to create signals up to 9 GHz on 16 synchronous output ports, while synchronously analyzing responses on 16 input ports. Presto has 16 DC-bias outputs, four inputs and four outputs for digital triggers or markers, and two continuous-wave outputs for synthesizing frequencies up to 15 GHz. Scaling to a large number of qubits is enabled through deterministic synchronization of multiple Presto units. A Python application programming interface configures a firmware for synthesis and analysis of pulses, coordinated by an event sequencer. The analysis integrates template matching (matched filtering) and low-latency (184–254 ns) feedback to enable a wide range of multi-qubit experiments. We demonstrate Presto’s capabilities with experiments on a sample consisting of two superconducting qubits connected via a flux-tunable coupler. We show single-shot readout and active reset of a single qubit; randomized benchmarking of single-qubit gates showing 99.972% fidelity, limited by the coherence time of the qubit; and calibration of a two-qubit iSWAP gate.

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Bashkirov, Eugene K. "Entanglement between two charge qubits taking account the Kerr media." Physics of Wave Processes and Radio Systems 27, no. 1 (March 29, 2024): 26–34. http://dx.doi.org/10.18469/1810-3189.2024.27.1.26-34.

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Background. The need to implement controlled coupling between qubits, which are the logical elements of quantum devices such as quantum computers and quantum networks, requires, along with the use of traditional methods, the development of new, more effective ways to organize the interaction of qubits with the microwave fields of resonators used to generate and control the entanglement of qubits. As one of these methods, a method based on the influence of frequency-regulated radio frequency signals on a superconducting Josephson qubit connected by a large Josephson junction to a free qubit has been proposed. Aim. The influence of the Kerr medium of the resonator, in which one of the two qubits is placed, on their entanglement induced by the coherent or thermal frequency-regulated radio frequency field of the resonator is considered. Methods. To analyze the dynamics of the system under consideration, the solution of the quantum Liouville equation for the full density matrix is studied. An exact solution o this equation is found in the case of initial separable and entangled states of qubits. The exact solution of the evolution equation is used to calculate the criterion of qubit-qubit entanglement – cconcurrence. Numerical modeling of the concurrence was carried out for various states of qubits, coherent and thermal fields of the resonator, as well as various values of the intensity of the resonator field and the Kerr nonlinearity parameter. Results. It is shown that for separable initial states of qubits, the inclusion of Kerr nonlinearity reduces the maximum degree of entanglement of qubits. For an entangled initial state of qubits, the possibility of creating long-lived entangled states in the presence of Kerr nonlinearity is shown. Conclusion. The type of initial states of qubits and the range of values of the intensities of the resonator fields and the Kerr nonlinearity parameters have been established, for which the most effective control and operation of the evolution of qubits, as well as the degree of their entanglement, in the physical system under consideration, is possible.

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Xu, Yilun, Gang Huang, David I. Santiago, and Irfan Siddiqi. "Radio frequency mixing modules for superconducting qubit room temperature control systems." Review of Scientific Instruments 92, no. 7 (July 1, 2021): 075108. http://dx.doi.org/10.1063/5.0055906.

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Park, Kun Hee, Yung Szen Yap, Yuanzheng Paul Tan, Christoph Hufnagel, Long Hoang Nguyen, Karn Hwa Lau, Patrick Bore, et al. "ICARUS-Q: Integrated control and readout unit for scalable quantum processors." Review of Scientific Instruments 93, no. 10 (October 1, 2022): 104704. http://dx.doi.org/10.1063/5.0081232.

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We present a control and measurement setup for superconducting qubits based on the Xilinx 16-channel radio-frequency system-on-chip (RFSoC) device. The proposed setup consists of four parts: multiple RFSoC boards, a setup to synchronize every digital to analog converter (DAC) and analog to digital converter (ADC) channel across multiple boards, a low-noise direct current supply for tuning the qubit frequency, and cloud access for remotely performing experiments. We also designed the setup to be free of physical mixers. The RFSoC boards directly generate microwave pulses using sixteen DAC channels up to the third Nyquist zone, which are directly sampled by its eight ADC channels between the fifth and the ninth zones.

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Gely, Mario F., Marios Kounalakis, Christian Dickel, Jacob Dalle, Rémy Vatré, Brian Baker, Mark D. Jenkins, and Gary A. Steele. "Observation and stabilization of photonic Fock states in a hot radio-frequency resonator." Science 363, no. 6431 (March 7, 2019): 1072–75. http://dx.doi.org/10.1126/science.aaw3101.

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Detecting weak radio-frequency electromagnetic fields plays a crucial role in a wide range of fields, from radio astronomy to nuclear magnetic resonance imaging. In quantum optics, the ultimate limit of a weak field is a single photon. Detecting and manipulating single photons at megahertz frequencies presents a challenge because, even at cryogenic temperatures, thermal fluctuations are appreciable. Using a gigahertz superconducting qubit, we observed the quantization of a megahertz radio-frequency resonator, cooled it to the ground state, and stabilized Fock states. Releasing the resonator from our control, we observed its rethermalization with nanosecond resolution. Extending circuit quantum electrodynamics to the megahertz regime, we have enabled the exploration of thermodynamics at the quantum scale and allowed interfacing quantum circuits with megahertz systems such as spin systems or macroscopic mechanical oscillators.

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THOMAS, Candice, Jean-Philippe Michel, Edouard Deschaseaux, Jean Charbonnier, Richard Souil, Elisa Vermande, Alain Campo, et al. "Superconducting routing platform for large-scale integration of quantum technologies." Materials for Quantum Technology, August 10, 2022. http://dx.doi.org/10.1088/2633-4356/ac88ae.

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Abstract To reach large-scale quantum computing, three-dimensional integration of scalable qubit arrays and their control electronics in multi-chip assemblies is promising. Within these assemblies, the use of superconducting interconnections, as routing layers, offers interesting perspective in terms of (1) thermal management to protect the qubits from control electronics self-heating, (2) passive device performance with significant increase of quality factors and (3) density rise of low and high frequency signals thanks to minimal dispersion. We report on the fabrication, using 200 mm silicon wafer technologies, of a multi-layer routing platform designed for the hybridation of spin qubit and control electronics chips. A routing level couples the qubits and the control circuits through one layer of Al0.995Cu0.005 and superconducting layers of TiN, Nb or NbN, connected between them by W-based vias. Wafer-level parametric tests at 300 K validate the yield of these technologies while low temperature electrical measurements in cryostat are used to extract the superconducting properties of the routing layers. Preliminary low temperature radio-frequency characterizations of superconducting passive elements, embedded in these routing levels, are presented.

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Kounalakis, Marios, Yaroslav M. Blanter, and Gary A. Steele. "Synthesizing multi-phonon quantum superposition states using flux-mediated three-body interactions with superconducting qubits." npj Quantum Information 5, no. 1 (November 21, 2019). http://dx.doi.org/10.1038/s41534-019-0219-y.

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AbstractMassive mechanical resonators operating at the quantum scale can enable a large variety of applications in quantum technologies as well as fundamental tests of quantum theory. Of crucial importance in that direction is both their integrability into state-of-the-art quantum platforms as well as the ability to prepare them in generic quantum states using well-controlled high-fidelity operations. Here, we propose a scheme for controlling a radio-frequency mechanical resonator at the quantum scale using two superconducting transmon qubits that can be integrated on the same chip. Specifically, we consider two qubits coupled via a capacitor in parallel to a superconducting quantum interference device (SQUID), which has a suspended mechanical beam embedded in one of its arms. Following a theoretical analysis of the quantum system, we find that this configuration, in combination with an in-plane magnetic field, can give rise to a tuneable three-body interaction in the single-photon strong-coupling regime, while enabling suppression of the stray qubit-qubit coupling. Using state-of-the-art parameters and qubit operations at single-excitation levels, we numerically demonstrate the possibility of ground-state cooling as well as high-fidelity preparation of mechanical quantum states and qubit-phonon entanglement, i.e. states having negative Wigner functions and obeying non-classical correlations. Our work significantly extends the quantum control toolbox of radio-frequency mechanical resonators and may serve as a promising architecture for integrating such mechanical elements with transmon-based quantum processors.

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Kelly, Eoin G., Alexei Orekhov, Nico W. Hendrickx, Matthias Mergenthaler, Felix J. Schupp, Stephan Paredes, Rafael S. Eggli, et al. "Capacitive crosstalk in gate-based dispersive sensing of spin qubits." Applied Physics Letters 123, no. 26 (December 25, 2023). http://dx.doi.org/10.1063/5.0177857.

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In gate-based dispersive sensing, the response of a resonator attached to a quantum dot gate is detected by a reflected radio frequency signal. This enables fast readout of spin qubits and tune up of arrays of quantum dots but comes at the expense of increased susceptibility to crosstalk, as the resonator can amplify spurious signals and induce fluctuations in the quantum dot potential. We attach tank circuits with superconducting NbN inductors and internal quality factors Qi>1000 to the interdot barrier gate of silicon double quantum dot devices. Measuring the interdot transition in transport, we quantify radio frequency crosstalk that results in a ring-up of the resonator when neighboring plunger gates are driven with frequency components matching the resonator frequency. This effect complicates qubit operation and scales with the loaded quality factor of the resonator, the mutual capacitance between device gate electrodes, and with the inverse of the parasitic capacitance to ground. Setting qubit frequencies below the resonator frequency is expected to substantially suppress this type of crosstalk.

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9

Dijck, Elwin A., Christian Warnecke, Malte Wehrheim, Ruben B. Henninger, Julia Eff, Kostas Georgiou, Andrea Graf, et al. "Sympathetically cooled highly charged ions in a radio-frequency trap with superconducting magnetic shielding." Review of Scientific Instruments 94, no. 8 (August 1, 2023). http://dx.doi.org/10.1063/5.0160537.

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We sympathetically cool highly charged ions (HCI) in Coulomb crystals of Doppler-cooled Be+ ions confined in a cryogenic linear Paul trap that is integrated into a fully enclosing radio-frequency resonator manufactured from superconducting niobium. By preparing a single Be+ cooling ion and a single HCI, quantum logic spectroscopy toward frequency metrology and qubit operations with a great variety of species are enabled. While cooling down the assembly through its transition temperature into the superconducting state, an applied quantization magnetic field becomes persistent, and the trap becomes shielded from subsequent external electromagnetic fluctuations. Using a magnetically sensitive hyperfine transition of Be+ as a qubit, we measure the fractional decay rate of the stored magnetic field to be at the 10−10 s−1 level. Ramsey interferometry and spin-echo measurements yield coherence times of >400 ms, demonstrating excellent passive magnetic shielding at frequencies down to DC.

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Kalboussi, Y., B. Delatte, S. Bira, K. Dembele, X. Li, F. Miserque, N. Brun, et al. "Reducing two-level systems dissipations in 3D superconducting niobium resonators by atomic layer deposition and high temperature heat treatment." Applied Physics Letters 124, no. 13 (March 25, 2024). http://dx.doi.org/10.1063/5.0202214.

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Superconducting qubits have arisen as a leading technology platform for quantum computing, which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency niobium resonators by atomic layer deposition of a 10 nm aluminum oxide Al2O3 thin films, followed by a high vacuum heat treatment at 650 °C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by x-ray photoelectron spectroscopy plus scanning and conventional high resolution transmission electron microscopy coupled with electron energy loss spectroscopy and energy dispersive spectroscopy, we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3.

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Wang, Changqing, Ivan Gonin, Anna Grassellino, Sergey Kazakov, Alexander Romanenko, Vyacheslav P. Yakovlev, and Silvia Zorzetti. "High-efficiency microwave-optical quantum transduction based on a cavity electro-optic superconducting system with long coherence time." npj Quantum Information 8, no. 1 (December 21, 2022). http://dx.doi.org/10.1038/s41534-022-00664-7.

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AbstractFrequency conversion between microwave and optical photons is a key enabling technology to create links between superconducting quantum processors and to realize distributed quantum networks. We propose a microwave-optical transduction platform based on long-coherence time superconducting radio-frequency (SRF) cavities coupled to electro-optic optical cavities to mitigate the loss mechanisms that limit the attainment of high conversion efficiency. We optimize the microwave-optical field overlap and optical coupling losses in the design while achieving long microwave and optical photon lifetime at milli-Kelvin temperatures. This represents a significant enhancement of the transduction efficiency up to 50% under incoming pump power of 140 μW, which allows the conversion of few-photon quantum signals. Furthermore, this scheme exhibits high resolution for optically reading out the dispersive shift induced by a superconducting transmon qubit coupled to the SRF cavity. We also show that low microwave losses enhance the fidelity of heralded entanglement generation between two remote quantum systems. Finally, high precision in quantum sensing can be reached below the standard quantum limit.

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Hampel, Benedikt, Daniel H. Slichter, Dietrich Leibfried, Richard P. Mirin, Sae Woo Nam, and Varun B. Verma. "Trap-integrated superconducting nanowire single-photon detectors with improved rf tolerance for trapped-ion qubit state readout." Applied Physics Letters 122, no. 17 (April 24, 2023). http://dx.doi.org/10.1063/5.0145077.

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State readout of trapped-ion qubits with trap-integrated detectors can address important challenges for scalable quantum computing, but the strong radio frequency (rf) electric fields used for trapping can impact detector performance. Here, we report on NbTiN superconducting nanowire single-photon detectors (SNSPDs) employing grounded aluminum mirrors as electrical shielding that are integrated into linear surface-electrode rf ion traps. The shielded SNSPDs can be operated at applied rf trapping potentials of up to 54 V peak at 70 MHz and temperatures of up to 6 K, with a maximum system detection efficiency of 68%. This performance should be sufficient to enable parallel high-fidelity state readout of a wide range of trapped ion species in a typical cryogenic apparatus.

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13

Yang, Ming, XiaoLiang He, WanPeng Gao, JunFeng Chen, Yu Wu, XiaoNi Wang, Gang Mu, Wei Peng, and ZhiRong Lin. "Kinetic inductance compact resonator with NbTiN micronwires." AIP Advances 14, no. 8 (August 1, 2024). http://dx.doi.org/10.1063/5.0220296.

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Nonlinear resonators of superconducting thin-film kinetic inductance have attracted considerable research interest in the fields of detectors, qubits, parametric amplifiers, and more. By tuning the deposition parameters, niobium titanium nitride (NbTiN) films (∼12 nm in thickness) present high resistivity(∼2000 μΩ cm) and large sheet kinetic inductance (∼0.7 nH/□). We designed resonators with NbTiN micronwire as the inductor and aluminum as the capacitor, which result in a high internal quality factor and a Kerr nonlinearity of a few hertz. The radio frequency response of the resonators demonstrates nonlinear behavior similar to that of the cubic Duffing oscillator, including frequency shift and hysteresis region. The kinetic inductance resonator is a promising candidate for high saturation power parametric amplifiers.

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Vigneau, Florian, Federico Fedele, Anasua Chatterjee, David Reilly, Ferdinand Kuemmeth, M. Fernando Gonzalez-Zalba, Edward Laird, and Natalia Ares. "Probing quantum devices with radio-frequency reflectometry." Applied Physics Reviews 10, no. 2 (February 24, 2023). http://dx.doi.org/10.1063/5.0088229.

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Many important phenomena in quantum devices are dynamic, meaning that they cannot be studied using time-averaged measurements alone. Experiments that measure such transient effects are collectively known as fast readout. One of the most useful techniques in fast electrical readout is radio-frequency reflectometry, which can measure changes in impedance (both resistive and reactive) even when their duration is extremely short, down to a microsecond or less. Examples of reflectometry experiments, some of which have been realized and others so far only proposed, include projective measurements of qubits and Majorana devices for quantum computing, real-time measurements of mechanical motion, and detection of non-equilibrium temperature fluctuations. However, all of these experiments must overcome the central challenge of fast readout: the large mismatch between the typical impedance of quantum devices (set by the resistance quantum) and of transmission lines (set by the impedance of free space). Here, we review the physical principles of radio-frequency reflectometry and its close cousins, measurements of radio-frequency transmission and emission. We explain how to optimize the speed and sensitivity of a radio-frequency measurement and how to incorporate new tools, such as superconducting circuit elements and quantum-limited amplifiers into advanced radio-frequency experiments. Our aim is threefold: to introduce the readers to the technique, to review the advances to date, and to motivate new experiments in fast quantum device dynamics. Our intended audience includes experimentalists in the field of quantum electronics who want to implement radio-frequency experiments or improve them, together with physicists in related fields who want to understand how the most important radio-frequency measurements work.

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Stanley, Manoj, Xiaobang Shang, Murat Celep, Martin Salter, Sebastian de Graaf, Tobias Lindstrom, Sang-Hee Shin, et al. "RF and microwave metrology for quantum computing – recent developments at the UK’s National Physical Laboratory." International Journal of Microwave and Wireless Technologies, April 25, 2024, 1–9. http://dx.doi.org/10.1017/s1759078724000369.

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Abstract Development of large-scale quantum computing systems will require radio frequency (RF) and microwave technologies operating reliably at cryogenic temperatures down to tens of milli-Kelvin (mK). The quantum bits in the most promising quantum computing technologies such as the superconducting quantum computing are designed using principles of microwave engineering and operated using microwave signals. The control, readout, and coupling of qubits are implemented using a network of microwave components operating at various temperature stages. To ensure reliable operation of quantum computing systems, it is critical to ensure optimal performance of these microwave components and qubits at their respective operating temperatures, which can be as low as mK temperatures. It is, therefore, critical to understand the microwave characteristics of waveforms, components, circuits, networks, and systems at cryogenic temperatures. The UK’s National Physical Laboratory (NPL) is focussed on developing new microwave measurement capabilities through the UK’s National Quantum Technologies Programme to address various microwave test and measurement challenges in quantum computing. This includes the development of various measurement capabilities to characterize the microwave performance of quantum and microwave devices and substrate materials at cryogenic temperatures. This paper summarizes the roadmap of activities at NPL to address these microwave metrology challenges in quantum computing.

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Journal articles on the topic 'Radio-Frequency superconducting qubit'

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