arXiv subjects

Nitzan Kahn

Publications and source records attributed to Nitzan Kahn.

4 recordsLinked to original sources

arXiv2026

Qubit Noise Sensing via Induced Photon Loss in a Superconducting Cavity

Characterizing noise in superconducting qubits is essential for improving coherence and gate performance. Conventional noise-sensing methods typically use the qubit itself as the sensor, which limits both accessible bandwidth and applicability during driven operation. Here, we demonstrate a method for measuring qubit frequency noise by converting it into photon loss in a coupled high-Q superconducting cavity. We use repeated mid-circuit qubit measurements with post-selection to separate this induced loss from intrinsic cavity decay. We validate the protocol using injected noise and show that the extracted loss scales as expected with the applied noise strength. Without added noise, we place an upper bound of $5\times10^3\,\mathrm{Hz}^2/\,\mathrm{Hz}$ on the qubit frequency-noise power spectral density at 508 MHz. The protocol opens access to a higher-frequency spectral window than standard qubit-based spectroscopy and may enable noise characterization during strong driving.

quant-ph↗

arXiv2024

Recovering Quantum Coherence of a Cavity Qubit Coupled to a Noisy Ancilla through Real-Time Feedback

Decoherence in qubits, caused by their interaction with a noisy environment, poses a significant challenge to the development of reliable quantum processors. A prominent source of errors arises from noise in coupled ancillas, which can quickly spread to qubits. By actively monitoring these noisy ancillas, it is possible to not only identify qubit decoherence events but also to correct these errors in real time. This approach is particularly beneficial for bosonic qubits, where the interaction with ancillas is a dominant source of decoherence. In this work, we uncover the intricate dynamics of decoherence in a superconducting cavity qubit due to its interaction with a noisy transmon ancilla. By tracking the noisy ancilla trajectory and using real-time feedback, we successfully recover the lost coherence of the cavity qubit, achieving a fivefold increase in its pure dephasing time. Additionally, by detecting ancilla errors and converting them into erasures, we improve the pure dephasing time by more than an order of magnitude. These advances are essential for realizing long-lived cavity qubits with high-fidelity gates, and they pave the way for more efficient bosonic quantum error-correction codes.

quant-ph↗

arXiv2023

Superconducting cavity qubit with tens of milliseconds single-photon coherence time

Storing quantum information for an extended period of time is essential for running quantum algorithms with low errors. Currently, superconducting quantum memories have coherence times of a few milliseconds, and surpassing this performance has remained an outstanding challenge. In this work, we report a qubit encoded in a novel superconducting cavity with a coherence time of 34 ms, an improvement of over an order of magnitude compared to previous demonstrations. We use this long-lived quantum memory to store a Schr\"odinger cat state with a record size of 1024 photons, indicating the cavity's potential for bosonic quantum error correction.

quant-ph↗

arXiv2022

Tomography of Feshbach Resonance States

Feshbach resonances are fundamental to interparticle interactions and become particularly important in cold collisions with atoms, ions, and molecules. Here we present the detection of Feshbach resonances in a benchmark system for strongly interacting and highly anisotropic collisions -- molecular hydrogen ions colliding with noble gas atoms. The collisions are launched by cold Penning ionization exclusively populating Feshbach resonances that span both short- and long-range parts of the interaction potential. We resolved all final molecular channels in a tomographic manner using ion-electron coincidence detection. We demonstrate the non-statistical nature of the final state distribution. By performing quantum scattering calculations on ab initio potential energy surfaces, we show that the isolation of the Feshbach resonance pathways reveals their distinctive fingerprints in the collision outcome.

physics.atom-ph↗