arXiv subjects

Konstantin Kalashnikov

Publications and source records attributed to Konstantin Kalashnikov.

4 recordsLinked to original sources

arXiv2023

Fluxonium Qubits in a Flip-Chip Package

The strong anharmonicity and high coherence times inherent to fluxonium superconducting circuits are beneficial for quantum information processing. In addition to requiring high-quality physical qubits, a quantum processor needs to be assembled in a manner that minimizes crosstalk and decoherence. In this paper, we report work on fluxonium qubits packaged in a flip-chip architecture, where a classical control and readout chip is bump-bonded to the quantum chip, forming a multi-chip module (MCM). The modular approach allows for improved connectivity between the qubits and control/readout elements, and separate fabrication processes. We characterize the coherence properties of the individual fluxonium qubits, demonstrate high fidelity single-qubit gates with 6 ns microwave pulses (without DRAG), and identify the main decoherence mechanisms to improve on the reported results.

quant-ph↗

arXiv2021

Phase Diffusion in Low-$E_J$ Josephson Junctions at milli-Kelvin Temperatures

Josephson junctions (JJs) with Josephson energy $E_J \lesssim 1K$ are widely employed as non-linear elements in superconducting circuits for quantum computing, operating at milli-Kelvin temperatures. Here we experimentally study incoherent phase slips (IPS) in low-$E_J$ Aluminum-based JJs at $T<0.2K$, where the IPS become the dominant source of dissipation. We observed strong suppression of the critical (switching) current and a very rapid growth of the zero-bias resistance with decreasing Josephson energy below $E_J \sim 1K$. This behavior is attributed to the IPSs whose rate exponentially increases with decreasing the ratio $E_J/T$. Our observations are in line with other data reported in literature. With further improvement of coherence of superconducting qubits, the observed dissipation from IPS might limit the performance of qubits based on low-$E_J$ junctions.

cond-mat.supr-con↗

arXiv2020

Granular Aluminum Meandered Superinductors for Quantum Circuits

We have designed superinductors made of strongly disordered superconductors for implementation in "hybrid" superconducting quantum circuits. The superinductors have been fabricated as meandered nanowires made of granular Aluminum films. Optimization of the device geometry enabled realization of superinductors with the inductance $\sim 1 μH$ and the self-resonance frequency over 3 GHz. These compact superinductors are attractive for a wide range of applications, from superconducting circuits for quantum computing to microwave elements of cryogenic parametric amplifiers and kinetic-inductance photon detectors.

cond-mat.mes-hall↗

arXiv2019

Bifluxon: Fluxon-Parity-Protected Superconducting Qubit

We have developed and characterized a symmetry-protected superconducting qubit that offers simultaneous exponential suppression of energy decay from charge and flux noise, and dephasing from flux noise. The qubit consists of a Cooper-pair box (CPB) shunted by a superinductor, thus forming a superconducting loop. Provided the offset charge on the CPB island is an odd number of electrons, the qubit potential corresponds to that of a $\cos ϕ/ 2$ Josephson element, preserving the parity of fluxons in the loop via Aharonov-Casher interference. In this regime, the logical-state wavefunctions reside in disjoint regions of phase space, thereby ensuring the protection against energy decay. By switching the protection on, we observed a ten-fold increase of the decay time, reaching up to $100 μ\mathrm{s}$. Though the qubit is sensitive to charge noise, the sensitivity is much reduced in comparison with the charge qubit, and the charge-noise-induced dephasing time of the current device exceeds $1 μ\mathrm{s}$. Implementation of the full dephasing protection can be achieved in the next-generation devices by combining several $\cos ϕ/ 2$ Josephson elements in a small array.

cond-mat.supr-con↗