Inductively shunted transmon qubit with tunable transverse and longitudinal coupling

We present the design of an inductively shunted transmon qubit with flux-tunable coupling to an embedded harmonic mode. This circuit construction offers the possibility to flux-choose between pure transverse and pure longitudinal coupling, that is coupling to the $\sigma_x$ or $\sigma_z$ degree of freedom of the qubit. While transverse coupling is the coupling type that is most commonly used for superconducting qubits, the inherently different longitudinal coupling has some remarkable advantages both for readout and for the scalability of a circuit. Being able to choose between both kinds of coupling in the same circuit provides the flexibility to use one for coupling to the next qubit and one for readout, or vice versa. We provide a detailed analysis of the system's behavior using realistic parameters, along with a proposal for the physical implementation of a prototype device.Comment: 14 pages, 14 figure

An argon ion beam milling process for native AlOx\text{AlO}_\text{x} layers enabling coherent superconducting contacts

We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits. From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50$\,\mathrm{m}\Omega \cdot \mu \mathrm{m}^2$ at a frequency of 4.5 GHz. Resonators for which only $6\%$ of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic field, showed quality factors above $10^6$ in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing.Comment: 4 pages, 4 figures, supplementary materia

Quasiparticle dynamics in granular aluminum close to the superconductor to insulator transition

Superconducting high kinetic inductance elements constitute a valuable resource for quantum circuit design and millimeter-wave detection. Granular aluminum (GrAl) in the superconducting regime is a particularly interesting material since it has already shown a kinetic inductance in the range of nH$/\Box$ and its deposition is compatible with conventional Al/AlOx/Al Josephson junction fabrication. We characterize microwave resonators fabricated from GrAl with a room temperature resistivity of $4 \times 10^3\,\mu\Omega\cdot$cm, which is a factor of 3 below the superconductor to insulator transition, showing a kinetic inductance fraction close to unity. The measured internal quality factors are on the order of $Q_{\mathrm{i}} = 10^5$ in the single photon regime, and we demonstrate that non-equilibrium quasiparticles (QP) constitute the dominant loss mechanism. We extract QP relaxation times in the range of 1 s and we observe QP bursts every $\sim 20$ s. The current level of coherence of GrAl resonators makes them attractive for integration in quantum devices, while it also evidences the need to reduce the density of non-equilibrium QPs.Comment: 5 pages, 4 figures, supplementary materia

Non-degenerate parametric amplifiers based on dispersion engineered Josephson junction arrays

Determining the state of a qubit on a timescale much shorter than its relaxation time is an essential requirement for quantum information processing. With the aid of a new type of non-degenerate parametric amplifier, we demonstrate the continuous detection of quantum jumps of a transmon qubit with 90% fidelity in state discrimination. Entirely fabricated with standard two-step optical lithography techniques, this type of parametric amplifier consists of a dispersion engineered Josephson junction (JJ) array. By using long arrays, containing $10^3$ JJs, we can obtain amplification at multiple eigenmodes with frequencies below $10~\mathrm{GHz}$, which is the typical range for qubit readout. Moreover, by introducing a moderate flux tunability of each mode, employing superconducting quantum interference device (SQUID) junctions, a single amplifier device could potentially cover the entire frequency band between 1 and $10~\mathrm{GHz}$.Comment: P.W. and I.T. contributed equally. 9 pages, 5 figures and appendice

Demonstration of a parity-time symmetry breaking phase transition using superconducting and trapped-ion qutrits

Scalable quantum computers hold the promise to solve hard computational problems, such as prime factorization, combinatorial optimization, simulation of many-body physics, and quantum chemistry. While being key to understanding many real-world phenomena, simulation of non-conservative quantum dynamics presents a challenge for unitary quantum computation. In this work, we focus on simulating non-unitary parity-time symmetric systems, which exhibit a distinctive symmetry-breaking phase transition as well as other unique features that have no counterpart in closed systems. We show that a qutrit, a three-level quantum system, is capable of realizing this non-equilibrium phase transition. By using two physical platforms - an array of trapped ions and a superconducting transmon - and by controlling their three energy levels in a digital manner, we experimentally simulate the parity-time symmetry-breaking phase transition. Our results indicate the potential advantage of multi-level (qudit) processors in simulating physical effects, where additional accessible levels can play the role of a controlled environment.Comment: 14 pages, 9 figure

The Role of the Patriarch Hermogenes Written Applications in Organization of Zemstvo Militia, 1611

The article deals with a controversial issue in historical science about what specific role played by the Patriarch Hermogenes in the organization of the zemstvo movement during the Interregnum, at the beginning of the folding of the national militia at the end of December 1610 - January 1611. Researchers have repeatedly addressed this issue, since the first half of the XIX century, offering his vision and interpretation of information from sources, but so far the question of the existence of the patriarch of letters remains open. Unlike many conflicting evidence of narrative sources, the County assembly material correspondence deposited in the archive Solikamsk, gives us a ton more information. Analyzing the correspondence, we can trace what information and documents the city received sequentially from Nizhny Novgorod and then to the North and Siberia, as the correspondence was in XVI - XVII century in Muscovy. The correspondence contains the only mention of the patriarch of the charters, but in any document, we do not find even a brief retelling of their content, as was the case with other documents, which came on the ground during this period. Moreover, there are specific indications that the first two letters of the district from Smolensk and Moscow residents actually called “letters of the patriarch.” Comparison of evidence leads us to date the letter from Smolensk time drawing no earlier than December 29, 1610 and to refute the assumption of its of fake origin. Thus, Hermogenes, obviously, did not write letters on his behalf, but called for a protest against the Polish- Lithuanian interventionists in public speeches, personal contacts with fiduciaries messengers and sent the first two letters of initiative

Nondegenerate Parametric Amplifiers Based on Dispersion-Engineered Josephson-Junction Arrays

Determining the state of a qubit on a time scale much shorter than its relaxation time is an essential requirement for quantum information processing. With the aid of a nondegenerate parametric amplifier, we demonstrate the continuous detection of quantum jumps of a transmon qubit with 90% fidelity of state discrimination. Entirely fabricated by standard two-step optical-lithography techniques, this type of parametric amplifier consists of a dispersion-engineered Josephson-junction (JJ) array. By using long arrays, containing 10 3 JJs, we can obtain amplification in multiple eigenmodes with frequencies below 10 GHz, which is the typical range for qubit readout. Moreover, if a moderate flux tunability of each mode is introduced, employing superconducting-quantum-interference-device junctions, a single amplifier device could potentially cover the entire frequency band between 1 and 10 GHz