What is the Boundary between Quantum Physics and Classical Physics?
Marius Bild, Matteo Fadel, and Yu Yang and others from ETH Zurich University published a new article titled ‘Schrödinger Cat States of a 16-Microgram Mechanical Oscillator’ in Science on April 21st, 2023 [1].
In their article, they investigate the boundary between the macroscopic and microscopic worlds. As we know from quantum mechanics, the microscopic world does not obey the laws of classical physics. At small distances, quantum mechanics applies.
De Broglie’s law explains the dual nature of matter very well. It states that every particle with mass, including electrons, protons, and atoms, also has a wave-like nature. The law is expressed mathematically as λ = h/p, where λ is the particle’s wavelength, h is the Planck constant, and p is the particle’s momentum. This formula has important implications. It suggests that particles can exhibit wave-like behavior, and their wavelength is inversely proportional to their momentum. It also implies that particles can occupy certain energy levels in an atom, leading to the concept of quantized energy levels.
De Broglie’s law states that matter can exhibit quantum mechanical properties when its wavelength is comparable to its size or when it interacts with other particles or systems that have quantum mechanical properties
However, this law does not draw a distinct line between quantum and classical physics; instead, it provides a framework for understanding the dual nature of particles. De Broglie’s law describes the relationship between the momentum and wavelength of a particle, and it applies to both classical and quantum systems. However, it is in the realm of quantum mechanics that the wave-like behavior of matter becomes significant, and concepts such as wave-particle duality, superposition, and entanglement are necessary for understanding the behavior of particles at the subatomic level. This means that when the momentum is low enough, particles will obey quantum physics, while at high enough momentum, they will obey classical physics.
Bild et al. [1] set out to investigate the distinct boundary between the quantum and classical physics realms.
To do this, they prepared a mechanical resonator, which is a mechanical device that vibrates at a particular frequency. They created a superposition between 10¹⁷ individual atoms and investigated their decoherence dynamics. By controlling the size and phase of the superposition, they were able to investigate the boundary between quantum and classical physics.
They created a device called hBAR, which consists of a high-overtone bulk acoustic-wave resonator (hBAR), and used it to create a superposition state consisting of 10¹⁷ individual atoms. They then investigated the decoherence responses of the atoms with different sizes.
The researchers concluded that as the size of the atoms increased, the negativity and amount of entanglement between two systems decreased. However, due to the limited size of the cat states produced, they were not able to specify an exact distance at which quantum and classical physics discern. They stated, ‘The maximum size of the cat state that we can prepare is currently limited by our device parameters, including both the qubit and phonon decoherence rates.’
Although there is no clear answer to the limit between quantum and classical physics, we are getting closer to finding it. We do not have all the answers yet, but eventually, we will be able to solve the mysteries of the universe if we ask the right questions.
References
[1] M. Bild et al., “Schrödinger cat states of a 16-microgram mechanical oscillator,” Nov. 2022, doi: 10.1126/science.adf7553.
[2] “Louis De Broglie Kimdir? — Çılgın Fizikçiler ve Bilim İnsanları.” https://cilginfizikcilervbi.com/louis-de-broglie-kimdir/ (accessed Apr. 30, 2023).
[3] “Dual Behavior of Electromagnetic Radiation | Black Body Radiation, Byjus.” https://byjus.com/chemistry/dual-behaviour-electromagnetic-radiation/ (accessed Apr. 30, 2023).
