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Publications in Josephson Junctions by NOMIS researchers

Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours

NOMIS Researcher(s)

Published in

July 5, 2023

Currently available quantum processors are dominated by noise, which severely limits their applicability and motivates the search for new physical qubit encodings. In this work, we introduce the inductively shunted transmon, a weakly flux-tunable superconducting qubit that offers charge offset protection for all levels and a 20-fold reduction in flux dispersion compared to the state-of-the-art resulting in a constant coherence over a full flux quantum. The parabolic confinement provided by the inductive shunt as well as the linearity of the geometric superinductor facilitates a high-power readout that resolves quantum jumps with a fidelity and QND-ness of >90% and without the need for a Josephson parametric amplifier. Moreover, the device reveals quantum tunneling physics between the two prepared fluxon ground states with a measured average decay time of up to 3.5 h. In the future, fast time-domain control of the transition matrix elements could offer a new path forward to also achieve full qubit control in the decay-protected fluxon basis. © 2023, The Author(s).

Research field(s)
Natural Sciences, Physics & Astronomy, General Physics

DOI
10.1038/s41467-023-39656-2

Surpassing the Resistance Quantum with a Geometric Superinductor

NOMIS Researcher(s)

Published in

October 29, 2020

Superinductors have a characteristic impedance exceeding the resistance quantum RQ≈6.45kω, which leads to a suppression of ground-state charge fluctuations. Applications include the realization of hardware-protected qubits for fault-tolerant quantum computing, improved coupling to small-dipole-moment objects, and the definition of a new quantum-metrology standard for the ampere. In this work, we refute the widespread notion that superinductors can only be implemented based on kinetic inductance, i.e., using disordered superconductors or Josephson-junction arrays. We present the modeling, fabrication, and characterization of 104 planar aluminum-coil resonators with a characteristic impedance up to 30.9 kω at 5.6 GHz and a capacitance down to ≤1 fF, with low loss and a power handling reaching 108 intracavity photons. Geometric superinductors are free of uncontrolled tunneling events and offer high reproducibility, linearity, and the ability to couple magnetically – properties that significantly broaden the scope of future quantum circuits.

Research field(s)
Natural Sciences, Physics & Astronomy, Applied Physics

DOI
10.1103/PhysRevApplied.14.044055

Microwave quantum illumination with a digital phase-conjugated receiver

NOMIS Researcher(s)

Published in

September 21, 2020

Quantum illumination is a sensing technique that employs entangled signal-idler beams to improve the detection efficiency of low-reflectivity objects in environments with large thermal noise. The advantage over classical strategies is evident at low signal brightness, a feature which could make the protocol an ideal prototype for non-invasive scanning or low-power short-range radar. Here we experimentally investigate the concept of quantum illumination at microwave frequencies, by generating entangled fields using a Josephson parametric converter which are then amplified to illuminate a room-temperature object at a distance of 1 meter. Starting from experimental data, we simulate the case of perfect idler photon number detection, which results in a quantum advantage compared to the relative classical benchmark. Our results highlight the opportunities and challenges on the way towards a first room-temperature application of microwave quantum circuits.

Research field(s)
Applied Sciences, Information & Communication Technologies, Networking & Telecommunications

DOI
10.1109/RadarConf2043947.2020.9266397

Microwave quantum illumination using a digital receiver

NOMIS Researcher(s)

Published in

May 1, 2020

Quantum illumination uses entangled signal-idler photon pairs to boost the detection efficiency of low-reflectivity objects in environments with bright thermal noise. Its advantage is particularly evident at low signal powers, a promising feature for applications such as noninvasive biomedical scanning or low-power short-range radar. Here, we experimentally investigate the concept of quantum illumination at microwave frequencies. We generate entangled fields to illuminate a room-temperature object at a distance of 1 m in a free-space detection setup. We implement a digital phase-conjugate receiver based on linear quadrature measurements that outperforms a symmetric classical noise radar in the same conditions, despite the entanglement-breaking signal path. Starting from experimental data, we also simulate the case of perfect idler photon number detection, which results in a quantum advantage compared with the relative classical benchmark. Our results highlight the opportunities and challenges in the way toward a first room-temperature application of microwave quantum circuits.

Research field(s)
Health Sciences, Biomedical Research, Developmental Biology

DOI
10.1126/sciadv.abb0451

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