zero temperature symmetry breaking quantum chip

Quantum Leap: Zero-Temperature Symmetry Breaking Simulated on a Superconducting Quantum Chip

Landmark Quantum Experiment at Absolute Zero

For the first occasion, an international consortium of scientists has successfully replicated spontaneous symmetry breaking (SSB) at absolute zero on a superconducting quantum processor—achieving a fidelity exceeding 80% and marking a landmark in both quantum computing and condensed-matter physics.

The findings have been published in the journal Nature Communications.

A Collaborative Breakthrough in Quantum Computing

Beginning in a classical antiferromagnetic phase—with alternating spin orientations—the system later transformed into a ferromagnetic quantum phase, marked by uniformly aligned spins and the formation of quantum correlations.

From Anti-ferromagnetism to Quantum Ferromagnetism

"The system initially exhibited a flip-flop spin arrangement, which spontaneously evolved into a state where all spins aligned in the same direction. This transition, driven by symmetry breaking," was explained by Alan Santos—a physicist at the Institute of Fundamental Physics, CSIC and a co-leader of the theoretical team.

Alan Santos Explains the Transition Mechanism

At the time this work was carried out, Santos held a FAPESP postdoctoral fellowship at the Department of Physics, Federal University of São Carlos (UFSCar), São Paulo Brazil. The research was a collaborative effort involving scientists from UFSCar, the Southern University of Science and Technology in Shenzhen, China and Aarhus University in Denmark.

Theoretical Insights and Zero Temperature Modeling

Why Absolute Zero Cannot Be Physically Achieved

"The key breakthrough lay in simulating the dynamics at absolute zero," Santos explains. "Although similar transitions had been studied previously, they were always at non-zero temperatures. What we demonstrated is that, at zero temperature, symmetry breaking can occur even in local interactions between neighbouring particles."

It bears recalling that absolute zero is unattainable in practice, as it would require every particle in a material to be perfectly motionless. Instead, the team modelled the system's behaviour at this limit using quantum computing.

The Seven-Qubit Circuit Design and Experiment Execution

Their experiment deployed a seven-qubit circuit arranged so that only nearest-neighbour interactions occurred and an algorithm was run to emulate adiabatic evolution at zero temperature.

"We developed the circuit conceptually and it was the researchers in China who brought it to life in the laboratory," say Santos.

Detecting Quantum Phase Transition

The Role of Correlation Functions and Rényi Entropy

The phase transition was detected through correlation functions and Rényi entropy, which indicated the emergence of ordered structures and quantum entanglement.

Understanding Quantum Entanglement

Entanglement, a hallmark of quantum mechanics, describes a condition where two particles remain linked in such a way that the state of one immediately determines the state of the order, irrespective of the distance between them.

Rényi Entropy as a Diagnostic Tool

Rényi entropy, first proposed in the 1960s by Hungarian mathematician Alfréd R ényi (1921-1970), serves as a tool to assess the extent and distribution of entanglement within a quantum system. It enables us to gauge how strongly subsystems are entangled.

Superposition and Entanglement in Quantum Computing

Comparing Classical vs Quantum performance

According to Santos, the twin pillars of quantum computing are superposition and entanglement: "Superposition permits a quantum system to exist in multiple states at the same time, a property referred to as quantum parallelism. Entanglement represents a kind of correlation unattainable by classical machines."

Santos explains: "Think of having a number of keys and trying to discover which unlocks a door. A conventional computer would test each one in turn. A quantum computer, however, can try multiple keys at once, making the search far quicker."

Simulating Quantum Systems with Quantum Hardware

the practical difference between classical and quantum computers is primarily one of performance. Though both are theoretically capable of solving the same types of mathematical problems, the time required can differ dramatically. For instance, factoring large numbers into primes may take a classical computer millions of years, whereas a quantum system could achieve it far more swiftly.

Using a classical computer to simulate quantum systems can seem counter-intuitive and in some cases, it is entirely unfeasible. The study demonstrated, however, that such simulations can be effectively performed using quantum computing resources.

Significance of the Research Location and Qubit Implementation

Southern University of Science and Technology, Shenzhen

The experiment took place at the Southern University of Science and Technology in Shenzhen—now regarded as one of the world's foremost centres of science, technology and industry. Designated China's first "special economic zone" in 1980, the city has transformed from a modest fishing village of 30,000 into a thriving metropolis or more than 17 million and hosts global market-leading firms.

Scalability of Superconducting Qubits

Superconducting qubits, composed of aluminium and niobium alloys and operating at roughly one millikelvin, were employed the implementation. "Their key advantage is scalability. In principle, we can manufactures chips containing hundreds," says Santos.

Symmetry and Its Foundational Role in Physics

How Symmetry and Its Breaking Shape Physical Laws

The notion of symmetry breaking is fundamental across every branch of physics. In fact, the entire framework of physics is built upon symmetries and the ways in which they are broken.

"Symmetry underpins the laws of conservation, while symmetry breaking enables the emergence of complex structures," explains Santos.

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