Qubit-based Device Passively Detects Schwinger Boson Dynamics and Enables Contactless Material Spectroscopy

The quest to understand complex materials receives a significant boost from a new approach to detecting subtle quantum phenomena, as demonstrated by Ioannis Petrides, Arpit Arora, and Prineha Narang from the University of California, Los Angeles. The team develops a novel device integrating a superconducting qubit with a microwave circuit, enabling the passive detection of dynamic processes in materials without the need for direct electrical contact. This breakthrough circumvents a major challenge in studying materials like van der Waals heterostructures, where establishing reliable electrical connections proves difficult. By carefully controlling the interaction between the qubit and the circuit, the researchers achieve a highly sensitive method for observing material properties, potentially unlocking access to previously elusive aspects of correlated materials and advancing our understanding of fundamental quantum behaviour.

Qubit Detection of Schwinger Boson Dynamics

Researchers have demonstrated a novel method for passively detecting the dynamics of Schwinger bosons, emergent excitations found in one-dimensional quantum systems, using a superconducting qubit. This work explores how a transmon qubit, coupled to a chain of interacting spins, responds to the motion of these bosons without direct qubit manipulation. The team observed a distinct spectral signature revealing the presence and behaviour of these bosons, establishing a new approach to investigate strongly correlated quantum systems and paving the way for advanced quantum sensors capable of detecting subtle quantum phenomena. This passive detection scheme preserves the coherence of the quantum system being studied, offering a significant advantage over traditional methods.

The research introduces an integrated photonic device where a transmon qubit capacitively couples to a microwave cross-resonator, enabling the sensing of time reversal broken order in materials. In this setup, the qubit functions as both a control element and a passive detector, while the cross-resonator hosts the sample, allowing for contactless spectroscopic analysis, particularly useful for materials where reliable electrical contacts are difficult to achieve, such as van der Waals 2D heterostructures. By tuning the coupling strength and phase between the qubit and resonator, the team successfully demonstrated the ability to sense material properties.

Quantum Materials Characterized via Circuit QED

This research focuses on the exploration of novel superconducting materials, particularly those exhibiting unconventional properties, and utilizes circuit quantum electrodynamics (cQED) as a powerful tool for their investigation. Superconducting circuits, including resonators and qubits, are designed and fabricated to interact with the quantum states of these materials, allowing researchers to probe and manipulate their properties. A key focus is the application of quantum geometry, specifically the geometric properties of the electronic band structure, to control and enhance superconducting behaviour. The team also investigates non-reciprocal behaviour in superconducting devices, crucial for building advanced quantum devices, and develops highly sensitive detectors, such as single-photon detectors, based on superconducting materials.

Extensive research has been conducted on magic-angle twisted bilayer graphene (MATBG), exploring its unconventional superconductivity, kinetic inductance, and superfluid density. Researchers are also investigating other 2D materials and heterostructures, including van der Waals cuprates, for superconductivity. Superconducting resonators are used as sensitive probes of material properties and as building blocks for quantum devices, while superconducting qubits are developed for quantum computing and sensing. The research explores the use of quantum geometry to control and enhance superconducting properties, designing circuits sensitive to the geometric features of materials.

Researchers are investigating the relationship between quantum geometry and superconductivity, employing cQED spectroscopy to probe the electronic structure and properties of materials. Resonance and kinetic inductance measurements are used to extract information about materials, including magic-angle twisted bilayer graphene, strontium titanate, van der Waals heterostructures, and niobium-doped strontium titanate. This research contributes to the advancement of quantum computing by developing more robust and scalable superconducting qubits. It also facilitates the discovery and characterization of new superconducting materials with improved properties, and enables the development of highly sensitive detectors for various quantum sensing applications. The research sheds light on the fundamental mechanisms behind superconductivity and the role of quantum geometry in material properties, potentially leading to technological innovations in areas such as energy, communications, and medicine.

Qubit-Resonator Hybrid Detects Material Properties

Researchers have demonstrated a new integrated photonic device combining a superconducting transmon qubit with a microwave cross-resonator, creating a platform for passively detecting quantum material properties. This device enables spectroscopic investigation of materials, particularly those where establishing reliable electrical contacts is challenging, such as van der Waals 2D heterostructures. By carefully controlling the interaction between the qubit and resonator, the team successfully encoded information about time reversal broken order within the dynamics of the qubit, allowing for its detection. The system’s sensitivity stems from tracking the hybridization of the resonator-qubit system, revealing changes induced by the material under investigation.

This approach offers a new means of probing materials without direct electrical contact, potentially unlocking access to the elusive properties of correlated materials. Further development, including the integration of advanced control techniques like machine learning for parameter optimization, could enhance the device’s precision and versatility. Future research directions include exploring the platform’s potential for investigating non-equilibrium systems and phase transitions, expanding the toolkit of microwave photonic devices for interacting with complex materials.