Unlocking the Quantum Realm: The Revolutionary Thermometer Measuring ‘Quantumness’ | Quanta Magazine

Understanding heat flow can be tricky, especially when it comes to the second law of thermodynamics. It states that heat moves naturally from hot objects to cold ones. But, as Brazilian physicist Alexssandre de Oliveira Jr. explains, there’s more to the story. Sometimes, in the quantum world, heat can actually flow from cold objects to hot ones. Sounds confusing? Let’s break it down.

Picture a warm cup of coffee next to a cold jug of milk. Normally, the heat will move from the coffee to the milk. This classic idea, introduced by Rudolf Clausius in 1850, holds true in everyday life. However, quantum mechanics shows us that at extremely small scales, the rules change. Here, heat can flow backwards, but this doesn’t mean the second law is broken; it’s just a special case addressed by quantum physics.

De Oliveira and his team have discovered that this unusual heat flow has practical benefits. They suggest it can help detect if an object is in a quantum state, like being in two different states at once (superposition) or being entangled with another object. This is crucial for quantum computing, where we want to ensure these quantum properties are being used effectively. Their method involves linking a quantum system to another that stores information, connected to a heat sink that absorbs energy. By measuring how much heat is transferred, scientists can monitor these quantum states.

This research opens up exciting avenues. It highlights how heat, energy, and information are intertwined. In this case, we “pay” for the unusual heat flow by losing some information about the quantum system. As Nicole Yunger Halpern, a physicist at the University of Maryland, puts it: “Thermodynamic quantities can signal quantum phenomena,” showing the deep connection between these fields.

This blend of thermodynamics and information isn’t new. In the 19th century, Scottish physicist James Clerk Maxwell introduced the idea of a “demon” that could sort molecules to create temperature differences, seemingly defying the second law. While scientists believed this was impossible, it took decades to uncover why. In 1961, Rolf Landauer showed that the demon’s memory would fill up, requiring erasure and thus more energy use, leading to increased entropy. This work marked the beginning of treating information as a thermodynamic resource.

Fast forward to today: quantum physics has given us tools and insights perfectly suited for advanced technologies like quantum computing. When particles are entangled, they share information in a way that can stretch classical thermodynamic principles. For instance, researchers found that heat can flow from cold to hot under specific quantum conditions. While this doesn’t fully overturn the second law—because it requires energy—the process uses the correlations between particles to drive this unusual flow.

Entangled particles can manipulate energy in ways that normal particles cannot. علماء like Časlav Brukner and Vlatko Vedral have shown that macroscopic thermodynamic measurements can hint at quantum entanglement—providing a bridge between the classical and quantum worlds. This crossover lets us extract more energy from quantum systems than from classical ones, challenging long-held scientific beliefs.

In short, quantum mechanics is not just a theoretical playground; it offers genuine opportunities to rethink energy flow, heat transfer, and even computing. While we may think we know how heat behaves, the quantum realm reveals a deeper, more complex story filled with potential.

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