arXiv subjects

Josiah Cochran

Publications and source records attributed to Josiah Cochran.

5 recordsLinked to original sources

arXiv2026

Practical Limits to Single-Mode Vacuum Squeezing with a SNAIL Parametric Amplifier

We characterize single-mode vacuum squeezing generated by a SNAIL Parametric Amplifier (SPA) operated under conditions representative of practical sensing and qubit-readout experiments. Motivated by prior expectations that Kerr-induced distortion limits squeezing in degenerate parametric amplifiers, we varied external flux and pump power to explore operating points where Kerr nonlinearity is theoretically minimized. We find that for practical applications where the squeezing frequency is fixed, the Kerr was variable by about a factor of two and the achievable squeezing showed no significant dependence on Kerr. Theoretical modeling supports this observation and indicates that baseline Kerr values in state-of-the-art SPAs are already too small to impose a practical limitation. Instead, squeezing was dominated by internal resonator loss and insertion loss in the microwave chain. These results indicate that, in practical SPAs, reducing loss, rather than suppressing Kerr, is the primary route to improved squeezing performance.

quant-ph↗

arXiv2025

Experimental signatures of a $\hat{Z}\hat{X}$ beam-splitter interaction between a Kerr-cat and transmon qubit

Quantum error correction (QEC) requires ancilla qubits to extract error syndromes from data qubits which store quantum information. However, ancilla errors can propagate back to the data qubits, introducing additional errors and limiting fault-tolerance. In superconducting quantum circuits, Kerr-cat qubits (KCQs), which exhibit strongly biased noise, have been proposed as ancillas to suppress this back-action and enhance QEC performance. Here, we experimentally demonstrate a beamsplitter interaction between a KCQ and a transmon, realizing an effective $\hat{Z}_{cat}\hat{X}_q$ coupling that can be employed for parity measurements in QEC protocols. We characterize the interaction across a range of cat sizes and drive amplitudes, confirming the expected scaling of the interaction rate. These results establish a step towards hybrid architectures that combine transmons as data qubits with noise-biased bosonic ancillas, enabling hardware-efficient syndrome extraction and advancing the development of fault-tolerant quantum processors.

quant-ph↗

arXiv2022

Strong coupling of a Gd$^{3+}$ multilevel spin system to an on-chip superconducting resonator

We report the realization of a strong coupling between a Gd$^{3+}$ spin ensemble hosted in a scheelite (CaWO$_4$) single crystal and the resonant mode of a coplanar stripline superconducting cavity leading to a large separation of spin-photon states of 146 MHz. The interaction is well described by the Dicke model and the crystal-field Hamiltonian of the multilevel spin system. We observe a change of the crystal-field parameters due to the presence of photons in the cavity that generates a significant perturbation of the crystal ground state. Using finite-element calculations, we numerically estimate the cavity sensing volume as well as the average spin-photon coupling strength of $g_0\approx$ 620 Hz. Lastly, the dynamics of the spin-cavity states are explored via pulsed measurements by recording the cavity ring-down signal as a function of pulse length and amplitude. The results indicate a potential method to initialize this multilevel system in its ground state via an active cooling process.

quant-ph↗

arXiv2022

Electronic DC-SQUID Emulator

Pulsed readout of Direct Current (DC) SUperconducting Quantum Interference Device (SQUID) is crucial for experiments which need to be performed at millikelvin temperatures, such as the readout of superconducting and electron spin based qubits. Pulsed readout algorithms used in these experiments are usually specific to the experimental setup and require some optimization. We present a circuit that emulates the behavior of a DC-SQUID in order to allow the development and evaluation of pulsed readout algorithms at room temperature without the need of a running dilution refrigerator. This novel circuit also constitutes a low cost device which can be used to teach the principles of a DC-SQUID in courses aimed at training the next generation of quantum engineers.

quant-ph↗

arXiv2021

Dual on-chip SQUID measurement protocol for flux detection in large magnetic fields

Sensitive magnetometers that can operate in high magnetic fields are essential for detecting magnetic resonance signals originating from small ensembles of quantum spins. Such devices have potential applications in quantum technologies, in particular quantum computing. We present a novel experimental setup implementing a differential flux measurement using two DC-SQUID magnetometers. The differential measurement allows for cancellation of background flux signals while enhancing sample signal. The developed protocol uses pulsed readout which minimizes on-chip heating since sub-Kelvin temperatures are needed to preserve quantum spin coherence. Results of a proof of concept experiment are shown as well.

cond-mat.mes-hall↗