Quantum Clock | 18 Nov 2025

Source: TH 

A 2025 study in Physical Review Letters has uncovered that in a quantum clock, the energy required to read the time is far greater than the energy required to make the clock tick, offering new perspectives in quantum physics, thermodynamics, and precision metrology. 

Quantum Clock 

• About: A quantum clock measures time using the behaviour of quantum particles, whose states change in tiny and probabilistic ways. 
  • Unlike classical clocks that always tick forward, quantum clocks show randomness, generate very little entropy (heat or disorder created when energy is used), and can even tick backward — raising the challenge of how they create a reliable and irreversible sense of time. 
• Working: A quantum clock operates using a Double Quantum Dot (DQD) system, consisting of two tiny electron-holding “islands” in a semiconductor.  
  • A single electron moves through them in the sequence 0 → L → R → 0, and this full cycle counts as one clock tick. 
  • The electron’s movement is controlled by voltages, and when forward and backward jumps become equal (equilibrium), no entropy is produced, and the device stops functioning as a clock. 
• Measurement:  To read the time, a nearby quantum dot acts as a charge sensor, and its current changes depending on whether the electron is in state 0, L, or R. 
  • Measuring the electron’s state uses energy, which creates a small amount of heat or disorder (entropy).  
• Significance: Could lead to more energy-efficient atomic clocks by focusing on reducing entropy in observation systems (e.g., optical clocks, ytterbium lattice clocks). 
  • It can also help improve ultra-precise clocks, guide efficient quantum computing designs.