Researchers Demonstrate Stable Quantum Entanglement with Dissipation Control

Aziza Almanakly and colleagues at Research Laboratory of Electronics, in collaboration with Chalmers University of Technology, MIT and Massachusetts Institute of Technology, have achieved driven-dissipative entanglement between two giant artificial atoms coupled to a waveguide. Their approach uses continuous-wave driving and correlated dissipation to generate and preserve remote entanglement, attaining a Bell-state fidelity of 0.89 ±0.02. The findings offer a key pathway towards building practical quantum networks by overcoming limitations associated with traditional entanglement schemes and demonstrating the viability of using driven dissipation in giant atom systems.

Correlated dissipation enables high-fidelity sustained entanglement in a superconducting system

Entanglement, a fundamental quantum phenomenon where two or more particles become linked and share the same fate, is crucial for advancements in quantum computing, communication, and sensing. Achieving high-fidelity entanglement, particularly over significant distances, remains a substantial challenge. Current methods often rely on coherent, reversible interactions between qubits, the basic units of quantum information, which necessitate exquisitely calibrated pulses to execute. These calibrations are sensitive to environmental noise and system imperfections, limiting the scalability and robustness of quantum networks. Almanakly and colleagues have demonstrated entanglement measures now achieve a Bell-state fidelity of 0.89 ±0.02, a sharp improvement over prior methods that demanded precise calibration of interactions. A vital threshold for viable quantum networks has been surpassed. Previous techniques struggled with maintaining entanglement stability without careful adjustments. Dr. Andreas Wallraff’s team and Dr. Johannes Fink engineered a superconducting system with giant artificial atoms and a waveguide, successfully suppressing individual dissipation to preserve the entangled state. This new approach exploits correlated dissipation, a process where energy loss actively creates and sustains the quantum link.

The team’s innovation lies in harnessing driven-dissipative protocols. Unlike traditional methods, this approach employs a continuous-wave drive, a constant electromagnetic signal, in conjunction with engineered dissipation. Dissipation, typically viewed as a detrimental process that destroys quantum coherence, is here strategically implemented to stabilise entanglement in protected (or ‘dark’) states. These dark states are immune to certain types of noise, enhancing the longevity of the entangled connection. Controlling qubit frequencies in situ allowed for energy loss stabilisation, sustaining entanglement in protected states and demonstrating a pathway towards stronger quantum information processing. The superconducting system maintains entanglement for a sustained period, evidenced by a measured coherence time of 29.5 microseconds for individual qubits. This coherence time represents the duration for which the quantum information remains protected from decoherence, a major obstacle in quantum information processing. A broadened Lorentzian feature, with a width of eight times the initial decay rate at zero detuning, was revealed by transmission spectroscopy, confirming maximal collective superradiance. This broadened feature indicates strong coupling between the artificial atoms and the waveguide, facilitating efficient entanglement distribution. Despite this substantial step forward, current results rely on a highly controlled laboratory environment and do not yet demonstrate entanglement durability against the noise inherent in larger, more complex quantum systems.

The artificial atoms themselves are superconducting circuits designed to behave as quantum two-level systems. Their ‘giant’ nature refers to their relatively large size and strong coupling to the electromagnetic field, enhancing their interaction with the waveguide. The waveguide acts as a conduit for photons, mediating the entanglement between the two atoms. By carefully engineering the dissipation within the system, the researchers effectively ‘steer’ the energy loss to create and maintain the desired entangled state. This is achieved through a specific design of the superconducting circuits and their coupling to a dissipative element, allowing for the selective removal of energy from unwanted states while preserving the entanglement.

Active energy loss suppression extends entanglement duration in artificial atoms

The foundations for a future quantum internet, a network capable of transmitting information with unparalleled security and speed, are currently being built. Such a network would leverage the principles of quantum mechanics to encrypt and transmit data, offering levels of security unattainable with classical communication methods. Driven dissipation was used by the team, actively controlling energy loss to forge and sustain the connection, sidestepping a vital limitation of existing entanglement methods. A Bell-state fidelity of 0.89 represents a sharp step forward, despite the inherent limitations where energy loss ultimately restricts how long entanglement can be maintained. This fidelity value indicates the quality of the entangled state, with 0.89 signifying a high degree of correlation between the two atoms. Improving this fidelity further is crucial for reliable quantum communication.

Giant artificial atoms have been engineered and linked via a waveguide, successfully distributing entanglement, a key resource for future quantum technologies. Remote entanglement was demonstrated using these giant artificial atoms and a waveguide, establishing a new technique reliant on carefully managing energy loss, rather than precise calibration of quantum interactions. This approach successfully suppressed unwanted energy loss from individual atoms, preserving the fragile quantum connection and offering a pathway towards more resilient quantum networks. The method allows for the creation of stable entangled states, potentially improving the scalability of quantum computing architectures. Scalability is a significant hurdle in quantum computing, as increasing the number of qubits while maintaining coherence and control is exceptionally difficult. This driven-dissipative approach offers a promising route towards building larger, more complex quantum systems.

The implications of this research extend beyond quantum communication. The ability to control and manipulate dissipation in superconducting systems could also lead to advancements in quantum sensing, where entangled states are used to enhance the precision of measurements. Furthermore, the principles demonstrated here could be applied to other physical platforms for quantum information processing, such as trapped ions or photonic systems. Future work will focus on extending the entanglement duration, increasing the distance over which entanglement can be distributed, and demonstrating the robustness of the system against realistic noise conditions. Addressing these challenges is essential for realising the full potential of quantum networks and unlocking the transformative capabilities of quantum technologies.

The researchers successfully distributed entanglement between two giant artificial atoms connected by a waveguide, achieving a Bell-state fidelity of 0.89. This demonstrates a viable method for creating entanglement that relies on managing energy loss within the system, rather than requiring precisely timed interactions. By suppressing individual energy loss, the entanglement was preserved, offering a potential means of building more stable and scalable quantum networks. The authors intend to extend the duration of entanglement and increase the distance over which it can be distributed as future work.