Foundations of quantum thermodynamics

7 problems

• Is super-extensive charging power possible with few-body interactions?

  Contested

  A quantum battery is a set of N small quantum cells that store energy; charging them together with collective interactions may be faster than charging each cell separately. How that speed-up can grow with N under realistic, few-body interactions is disputed.

• Maximal precision of a quantum clock per unit entropy

  Open

  A clock must waste energy to tick, and classical clocks become steadier only in proportion to the waste. A 2025 theory paper showed quantum clocks can become steadier exponentially faster, so the ultimate limit is open.

• Work fluctuations for quantum states with energy coherence

  Contested

  The usual way to measure work, measuring energy before and after, destroys superpositions between energy levels. A 2017 theorem showed no measurement scheme both keeps the standard results and gives the right average work for every state.

• Minimal time to cool a quantum system near absolute zero

  Partially resolved

  The third law says absolute zero cannot be reached in a finite number of steps. The open question is how fast the temperature can fall, given limited time or equipment, for the best possible refrigerator.

• Do quantum effects let heat engines outperform classical ones?

  Contested

  Engines made of a few atoms can use superposition or entanglement in their working parts. Whether this gives more power at the same efficiency than any classical engine with the same parts is disputed.

• Tight thermodynamic uncertainty relation for quantum machines

  Open

  In small classical machines, making a current steadier always costs extra wasted heat according to a fixed rule. Quantum machines can beat that rule, but by how much is unknown.

• Defining heat and work for strongly coupled quantum systems

  Contested

  When a small quantum system interacts strongly with its surroundings, the energy stored in the interaction cannot be cleanly assigned to either side. Several definitions of heat and work exist and they disagree.