New York University & IST Austria Map Radiative Noise

Researchers from New York University and the Institute of Science and Technology Austria have developed a new method for studying quantum systems, employing microwave radiometry to map radiative noise in a two-dimensional array of superconductor-semiconductor hybrid Josephson junctions. This approach allows for in-situ calibration of a sample’s circuit parameters and isolates the measurement from back-action effects, overcoming longstanding challenges in quantum measurement. Surprisingly, the team reports that the radiation temperature of the regime within the Josephson junction array is higher than both the quantum-critical and insulating regimes, a counterintuitive finding given expectations that resistance would make the insulating state the warmest. This work builds on recent efforts to understand non-equilibrium behavior in these systems, providing a measurement frequency one thousand times higher than previous work on low-frequency noise of an anomalous metallic system.

Josephson Junction Array Tuning Across Resistance Regimes Recent research reveals that the anomalous metallic regime of a Josephson junction array exhibits a higher “temperature” than both its quantum-critical and insulating counterparts; this challenges the expectation that increased resistance would correlate with greater heat. Researchers Kristen W. Léonard, Anton V. Bubis, Melissa Mikalsen, William F. Schiela, Bassel H. Elfeky, William M. Strickland, Duc Phan, Javad Shabani, and Andrew P. Higginbotham conducted this work. This approach represents a new experimental method for studying these complex quantum systems, allowing for in-situ calibration of the sample’s circuit parameters and isolation from measurement back-action effects.

The team’s work centers on understanding how these arrays transition between anomalous metallic, quantum-critical, and insulating states. The authors report observing excess radiation coincident with the onset of resistance saturation, indicating a departure from thermal equilibrium within the anomalous metallic phase. Converting this excess radiation into an equivalent temperature, they found the anomalous metal is demonstrably hotter than the other regimes and “more susceptible to heating.” Analysis of the quantum-critical regime revealed nonlinear scaling of radiative noise with applied bias, consistent with theoretical predictions of universal non-equilibrium behavior at quantum critical points. They suggest this indicates a broad regime with a unified non-equilibrium description near quantum criticality.

This research adds to a growing body of work exploring non-equilibrium behavior in quantum-critical systems, opening avenues for future exploration. Researchers are increasingly using microwave radiometry as a non-invasive technique for characterizing quantum materials, particularly those exhibiting complex behavior near phase transitions. Unlike traditional thermometry, which can disturb delicate quantum states, this approach leverages the natural blackbody radiation emitted by a sample to determine its temperature with improved accuracy. Kristen W. Léonard, Anton V. Bubis, Melissa Mikalsen, William F. Schiela, Bassel H. Elfeky, William M. Strickland, Duc Phan, Javad Shabani, and Andrew P. Higginbotham successfully developed a system that overcomes challenges in accurately probing these systems. This finding challenges intuition, as one might expect the insulating regime to be the warmest due to its resistance. Further analysis revealed the anomalous metallic regime potentially explains its emergence in systems where thermalization is incomplete. Researchers from Austria and New York University have developed a novel method for characterizing quantum materials, employing microwave radiometry to probe the anomalous metal regime found in Josephson junction arrays. The study revealed the anomalous metal exhibits a higher radiation temperature than both the quantum-critical and insulating states. Accurately measuring temperature within quantum materials is crucial for understanding emergent phenomena, and researchers have now deployed microwave radiometry to probe the thermal characteristics of the anomalous metal, a particularly enigmatic state of matter. Converting the excess microwave radiation into an equivalent temperature, the researchers found that the anomalous metal exhibited a higher thermal signature, challenging the expectation that insulating states would naturally generate the most heat due to resistance. This work, alongside recent studies of ultraclean graphene and heavy fermion strange metals, is opening new avenues for exploring non-equilibrium behavior in critical systems. Researchers pursuing a deeper understanding of quantum materials have long faced a challenge: accurately measuring a system’s properties without disturbing it.

The team of Kristen W. Léonard, Anton V. Bubis, Melissa Mikalsen, William F. Schiela, Bassel H. Elfeky, William M. Strickland, Duc Phan, Javad Shabani, and Andrew P. Higginbotham, along with colleagues at New York University and the University of Chicago, circumvented this issue with microwave radiometry. Crucially, the team leveraged established methodology from the calibration of axion haloscopes to accurately measure the temperature of emitted radiation. A circulator, a key component of the setup, ensures minimal disturbance to the delicate quantum state of the sample during measurement. This counters intuition, as the insulating state would typically be expected to exhibit the highest resistance and therefore, temperature. The researchers discovered the anomalous metallic regime is more susceptible to additional heating than other regimes, offering insight into its emergence within thermalized systems. This detailed analysis, coupled with the precise calibration, establishes a powerful new tool for investigating complex quantum phenomena. Researchers Kristen W. Léonard, Anton V. Bubis, Melissa Mikalsen, William F. Schiela, Bassel H. Elfeky, William M. Strickland, Duc Phan, Javad Shabani, and Andrew P. Higginbotham developed this technique, representing a significant advancement allowing in-situ calibration of circuit parameters and effectively isolating the sample from disruptive measurement back-action effects. Microwave radiometry is rapidly becoming a crucial tool for probing the subtle behaviors of quantum materials, offering a non-invasive method to study systems exhibiting anomalous metallic, quantum-critical, and insulating phases. Kristen W. Léonard, Anton V. Bubis, Melissa Mikalsen, William F. Schiela, Bassel H. Elfeky, William M. Strickland, Duc Phan, Javad Shabani, and Andrew P. Higginbotham explored theoretical predictions regarding non-equilibrium behavior at quantum critical points. Analyzing radiative noise as a function of applied bias, they found nonlinear scaling consistent with theoretical predictions, confirming predictions of universal non-equilibrium behavior.

The team focused on these hybrid junctions as a tunable model system, enabling investigation across anomalous metallic, quantum-critical, and insulating regimes. Beyond thermometry, the team explored non-equilibrium behavior near the superconductor-insulator phase transition. Establishing a steady state with applied bias, they found noise-equivalent radiation temperature scaling consistent with theoretical predictions, specifically the I√I relationship. The researchers attribute this to the anomalous metal being “more susceptible to heating than either the quantum critical or insulating regimes,” suggesting a fundamental difference in how energy dissipates within this phase. Beyond thermometry, the study delved into the non-equilibrium behavior near the superconductor-insulator transition. Source: http://link.aps.org/doi/10.1103/75bl-mm3b Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: