In a significant advance for quantum mechanics, a research team has successfully harnessed a process typically viewed as a barrier to quantum coherence to instead create robust, multipartite quantum entangled states. A group led by Prof. Lin Yiheng at the University of Science and Technology of China (USTC), in collaboration with Prof. Yuan Haidong of the Chinese University of Hong Kong, has demonstrated the ability to generate entanglement across two, three, and even five separate modes by strategically engineering dissipation. This counterintuitive approach, turning a problem into a solution, paves the way for more stable and scalable quantum technologies, with findings published in the journal Science Advances.
Multimode quantum entanglement is a cornerstone for the future of advanced technology, serving as a fundamental resource for quantum computing, secure communication, and ultra-precise sensing. However, the delicate nature of quantum states makes them extremely susceptible to environmental interference, or dissipation, which can destroy the quantum correlations necessary for these applications. For decades, the prevailing strategy was to meticulously isolate quantum systems from their surroundings, a complex and often impractical task. This new research inverts that paradigm. Instead of fighting dissipation, scientists are now controlling it, using a technique called dissipation engineering to guide a quantum system into a desired, highly entangled state and keep it there. This method establishes the target state as the system’s sole stable point, offering a powerful new tool for developing quantum information systems.
A New Paradigm in Quantum Control
The intentional use of dissipation marks a pivotal shift in quantum engineering. For years, the interaction of a quantum system with its environment was considered the primary antagonist in the quest to build functional quantum devices. This interaction, known as decoherence, unravels the fragile quantum states, leading to the loss of information and the breakdown of quantum computations. Consequently, immense effort has been invested in creating highly isolated environments, such as cryogenic chambers, to shield qubits from the disruptive noise of the outside world. While this approach has yielded successes, it presents significant scalability challenges.
From Obstacle to Instrument
Recent theoretical and experimental work has begun to re-evaluate the role of dissipation, suggesting that if it can be precisely controlled, it can become a valuable asset. This concept is at the heart of dissipation engineering. Instead of allowing the environment to randomly interfere with a quantum system, this technique designs a specific, engineered coupling between the system and its environment. The goal is to create a scenario where the dissipation actively pushes the system toward a specific target state. This process effectively removes entropy from the system that is induced by decoherence, making the desired quantum state the natural, steady end-point of the system’s evolution. This approach is analogous in some ways to adiabatic quantum computation, where a system is gently guided into a final state.
The Landmark USTC Experiment
The research conducted at USTC provides a compelling demonstration of this novel concept. The team successfully applied controlled dissipation to a multimode bosonic system, a significant step beyond previous experiments that were largely limited to single-mode or two-mode systems. Their setup allowed for programmable control over the dissipation processes, which was crucial for achieving their results.
High-Fidelity Multimode Entanglement
The primary achievement of the study was the generation of two-, three-, and five-mode squeezed entangled states. Squeezed states are a special type of quantum state where the uncertainty of one variable is reduced at the expense of increased uncertainty in another, and they are highly useful in precision measurement. The researchers started with initial thermal states, which are noisy and lack quantum correlations, and applied their dissipation engineering technique. The result was the successful creation of the target entangled states with a fidelity rating exceeding 84%, a remarkable level of accuracy that confirms the effectiveness of the method.
Autonomous Stabilization as a Key Feature
A particularly powerful aspect of the team’s platform is its “autonomous stabilization” capability. This means the system is engineered so that the highly entangled target state is the only stable configuration. Any other state the system might drift into is naturally driven back towards the desired entangled state by the controlled dissipation. This self-correcting mechanism is a major advantage for building robust quantum devices that can maintain their state over time without constant, active intervention, which is a significant hurdle for many current quantum computing architectures.
Broad Implications for Quantum Technology
The success of this experiment is not limited to a single type of quantum hardware. The principles of dissipation engineering are universal and can be adapted for a wide variety of physical platforms, suggesting its potential for broad impact across the entire field of quantum information science.
A Versatile and Scalable Method
The researchers note that their technique could be integrated into systems based on superconducting cavities, atomic ensembles, or nanomechanical oscillators. This versatility makes it an attractive tool for different research groups pursuing various paths to building a quantum computer. As quantum technology progresses toward greater integration and engineering maturity, the ability to generate stable entangled states through dissipation could provide essential support for these next-generation systems. It is poised to become a critical component in developing fault-tolerant quantum information processing.
Expanding the Frontiers of Dissipation Engineering
The work at USTC is part of a broader trend of exploring dissipation as a creative tool in quantum mechanics. Other research is investigating how engineered environments can produce entanglement in even more complex and non-intuitive scenarios, further pushing the boundaries of what is possible.
Entangling Distant and Unconnected Qubits
Some studies are exploring how dissipation can generate entanglement between quantum bits, or qubits, that are not directly interacting or even coupled to the same environment. This research shows that by using intermediate, coupled reservoirs, quantum correlations can be established between distant spins. This opens up possibilities for creating entanglement across larger, more distributed quantum networks without requiring a direct physical connection between every component.
Applications in Solid-State Systems
Another area of active research involves using dissipation to create long-lived entanglement in solid-state quantum systems. For instance, one proposed scheme aims to generate a form of many-body entanglement known as spin squeezing in an ensemble of solid-state qubits. In this model, a shared bath is driven into a non-equilibrium state, and the noise it emits is used to transfer quantum correlations to the qubits, driving them into an entangled state. Such approaches are particularly promising for quantum metrology, where entangled states are used to make measurements that surpass the limits of classical physics.
The Future of Engineered Quantum States
The collective progress in dissipation engineering represents a profound shift in how scientists approach the challenges of building a quantum future. By learning to work with environmental noise rather than simply trying to eliminate it, researchers are unlocking new and potentially more efficient pathways to generating the quantum resources necessary for next-generation technologies. This approach promises not only to make the creation of entangled states more robust but also to make the process more autonomous and less reliant on complex control systems. As these techniques are refined and applied to a wider range of physical systems, they could significantly accelerate the development of practical quantum computers, global quantum communication networks, and sensors with unprecedented precision. The era of treating the environment as an enemy of quantum mechanics may be giving way to a new age of partnership.