I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
29
Mä
2021
Superconducting Circuit Architecture for Digital-Analog Quantum Computing
We propose a superconducting circuit architecture suitable for digital-analog quantum computing (DAQC) based on an enhanced NISQ family of nearest-neighbor interactions. DAQC makesa smart use of digital steps (single qubit rotations) and analog blocks (parametrized multiqubit operations) to outperform digital quantum computing algorithms. Our design comprises a chain of superconducting charge qubits coupled by superconducting quantum interference devices (SQUIDs). Using magnetic flux control, we can activate/deactivate exchange interactions, double excitation/de-excitations, and others. As a paradigmatic example, we present an efficient simulation of an ℓ×h fermion lattice (with 2<ℓ≤h), using only 2(2ℓ+1)2+24 analog blocks. The proposed architecture design is feasible in current experimental setups for quantum computing with superconducting circuits, opening the door to useful quantum advantage with fewer resources.[/expand]
26
Mä
2021
Epitaxial Superconductor-Semiconductor Two-Dimensional Systems for Superconducting Quantum Circuits
Qubits on solid state devices could potentially provide the rapid control necessary for developing scalable quantum information processors. Materials innovation and design breakthroughs
have increased functionality and coherence of qubits substantially over the past two decades. Here we show by improving interface between InAs as a semiconductor and Al as a superconductor, one can reliably fabricate voltage-controlled Josephson junction field effect transistor (JJ-FET) that can be used as tunable qubits, resonators, and coupler switches. We find that band gap engineering is crucial in realizing a two-dimensional electron gas near the surface. In addition, we show how the coupling between the semiconductor layer and the superconducting contacts can affect qubit properties. We present the anharmonicity and coupling strengths from one and two-photon absorption in a quantum two level system fabricated with a JJ-FET.
Large Microwave Inductance of Granular Boron-Doped Diamond Superconducting Films
Boron-doped diamond granular thin films are known to exhibit superconductivity with an optimal critical temperature of Tc = 7.2K. Here we report the measured complex surface impedance
of Boron-doped diamond films in the microwave frequency range using a resonant technique. Experimentally measured inductance values are in good agreement with estimates obtained from the normal state sheet resistance of the material. The magnetic penetration depth temperature dependence is consistent with that of a fully-gapped s-wave superconductor. Boron-doped diamond films should find application where high kinetic inductance is needed, such as microwave kinetic inductance detectors and quantum impedance devices.
25
Mä
2021
Tomography in the presence of stray inter-qubit coupling
Tomography is an indispensable part of quantum computation as it enables diagnosis of a quantum process through state reconstruction. Existing tomographic protocols are based on determining
expectation values of various Pauli operators which typically require single-qubit rotations. However, in realistic systems, qubits often develop some form of unavoidable stray coupling making it difficult to manipulate one qubit independent of its partners. Consequently, standard protocols applied to those systems result in unfaithful reproduction of the true quantum state. We have developed a protocol, called coupling compensated tomography, that can correct for errors due to parasitic couplings completely in software and accurately determine the quantum state. We demonstrate the performance of our scheme on a system of two transmon qubits with always-on ZZ coupling. Our technique is a generic tomography tool that can be applied to large systems with different types of stray inter-qubit couplings and facilitates the use of arbitrary tomography pulses and even non-orthogonal axes of rotation.
22
Mä
2021
Random-access quantum memory using chirped pulse phase encoding
and quantum information"]processors [arXiv:1109.3743]. As in conventional computing, key attributes of such memories are high storage density and, crucially, random access, or the ability to read from or write to an arbitrarily chosen register. However, achieving such random access with quantum memories [arXiv:1904.09643] in a dense, hardware-efficient manner remains a challenge, for example requiring dedicated cavities per qubit [arXiv:1109.3743] or pulsed field gradients [arXiv:0908.0101]. Here we introduce a protocol using chirped pulses to encode qubits within an ensemble of quantum two-level systems, offering both random access and naturally supporting dynamical decoupling to enhance the memory lifetime. We demonstrate the protocol in the microwave regime using donor spins in silicon coupled to a superconducting cavity, storing up to four multi-photon microwave pulses and retrieving them on-demand up to 2~ms later. A further advantage is the natural suppression of superradiant echo emission, which we show is critical when approaching unit cooperativity. This approach offers the potential for microwave random access quantum memories with lifetimes exceeding seconds [arXiv:1301.6567, arXiv:2005.09275], while the chirped pulse phase encoding could also be applied in the optical regime to enhance quantum repeaters and networks.
21
Mä
2021
Metrological characterisation of non-Gaussian entangled states of superconducting qubits
Multipartite entangled states are significant resources for both quantum information processing and quantum metrology. In particular, non-Gaussian entangled states are predicted to
achieve a higher sensitivity of precision measurements than Gaussian states. On the basis of metrological sensitivity, the conventional linear Ramsey squeezing parameter (RSP) efficiently characterises the Gaussian entangled atomic states but fails for much wider classes of highly sensitive non-Gaussian states. These complex non-Gaussian entangled states can be classified by the nonlinear squeezing parameter (NLSP), as a generalisation of the RSP with respect to nonlinear observables, and identified via the Fisher information. However, the NLSP has never been measured experimentally. Using a 19-qubit programmable superconducting processor, here we report the characterisation of multiparticle entangled states generated during its nonlinear dynamics. First, selecting 10 qubits, we measure the RSP and the NLSP by single-shot readouts of collective spin operators in several different directions. Then, by extracting the Fisher information of the time-evolved state of all 19 qubits, we observe a large metrological gain of 9.89[Math Processing Error] dB over the standard quantum limit, indicating a high level of multiparticle entanglement for quantum-enhanced phase sensitivity. Benefiting from high-fidelity full controls and addressable single-shot readouts, the superconducting processor with interconnected qubits provides an ideal platform for engineering and benchmarking non-Gaussian entangled states that are useful for quantum-enhanced metrology.
Rapid and Unconditional Parametric Reset Protocol for Tunable Superconducting Qubits
Qubit initialization is critical for many quantum algorithms and error correction schemes, and extensive efforts have been made to achieve this with high speed and efficiency. Here
we experimentally demonstrate a fast and high fidelity reset scheme for tunable superconducting qubits. A rapid decay channel is constructed by modulating the flux through a transmon qubit and realizing a swap between the qubit and its readout resonator. The residual excited population can be suppressed to 0.08% ± 0.08% within 34 ns, and the scheme requires no additional chip architecture, projective measurements, or feedback loops. In addition, the scheme has negligible effects on neighboring qubits, and is therefore suitable for large-scale multi-qubit systems. Our method also offers a way of entangling the qubit state with an itinerant single photon, particularly useful in quantum communication and quantum network applications.
Josephson dynamical simulation using the electronic circuit simulator APLAC: a tutorial
Analysis Program for Linear Active Circuits (APLAC) is a general-purpose electronics circuit simulator, which has included a built-in model of the Josephson junction (JJ) since late
80’s. It capabilities in simulating eg. noisy Superconducting Quantum Interference Devices (SQUIDs), Rapid Single Flux Quantum (RSFQ) logic circuits, or Superconducting Transition Edge Sensors (TESes) are relatively unknown within the superconducting electronics community. Here we give a brief step-to-step tutorial for APLAC users to unleash those capabilities.
19
Mä
2021
Quantum sensing with superconducting circuits
Sensing and metrology play an important role in fundamental science and applications, by fulfilling the ever-present need for more precise data sets, and by allowing to make more reliable
conclusions on the validity of theoretical models. Sensors are ubiquitous, they are used in applications across a diverse range of fields including gravity imaging, geology, navigation, security, timekeeping, spectroscopy, chemistry, magnetometry, healthcare, and medicine. Current progress in quantum technologies inevitably triggers the exploration of quantum systems to be used as sensors with new and improved capabilities. This perspective initially provides a brief review of existing and tested quantum sensing systems, before discussing future possible directions of superconducting quantum circuits use for sensing and metrology: superconducting sensors including many entangled qubits and schemes employing Quantum Error Correction. The perspective also lists future research directions that could be of great value beyond quantum sensing, e.g. for applications in quantum computation and simulation.
The Anomalous Resonant Frequency Variation of Microwave Superconducting Niobium Cavities Near Tc
Superconducting radio-frequency (SRF) niobium cavities are the modern means of particle acceleration and an enabling technology for record coherence superconducting quantum systems
and ultra-sensitive searches for new physics. Here we report a systematic effect observed on a large set of bulk SRF cavities – an anomalous decrease of the resonant frequency at temperatures just below the superconducting transition temperature – which opens up a new means of understanding the physics behind nitrogen doping and other modern cavity surface treatments relevant for future quality factor and coherence improvements. The magnitude of the frequency change correlates systematically with the near-surface impurity distribution in studied cavities and with the observed Tc variation. We also present the first demonstration of the coherence peak in the real part of the AC complex conductivity in Nb SRF cavities and show that its magnitude varies with impurity distribution.