PHONONS

1. Context

2. What are Qubits?

• Quantum computers utilize qubits as their fundamental units of information.
• Qubits can be particles (e.g., electrons), collections of particles, or engineered quantum systems that mimic particle behavior.
• Quantum particles can exhibit unique behaviors governed by the rules of quantum physics, such as being in a superposition of 'on' and 'off' states simultaneously.
• Information can be encoded in specific properties of particles, like electron spin, to leverage their peculiar abilities.
• Quantum computers are expected to perform complex calculations surpassing the capabilities of today's best supercomputers.
• Linear optical quantum computing (LOQC) employs photons (particles of light) as qubits, using optical equipment like mirrors, lenses, and waveplates to process information.
• In theory, any particle controllable and manipulable through quantum-mechanical phenomena can serve as an information unit in a quantum computer.

• Researchers have explored the possibility of using phonons, packets of vibrational energy, as qubits in quantum computers.
• A recent study by the University of Chicago researchers introduced an acoustic beam splitter to manipulate phonons.
• Beam-splitters, commonly used in optics research, spilt a stream of photons into two beams by reflecting 50% of the photons and allowing the rest to pass through.
• The functioning of a beam-splitter relies on quantum physics when even shining photons one by one at the beam-spitter creates interference patterns.
• This phenomenon arises due to the wave-particle duality of particles and the superposition of quantum systems, where a single wave can exist in a superposition of reflected and transmitted states. 
• The development of tools for manipulating phonons opens up possibilities for building quantum computers with sound-based information units.

• Researchers developed an acoustic beam-splitter using a tiny comb-like device with 16 metal bars in a two-mm-long lithium niobate channel.
• The channel contained superconducting qubits capable of emitting and detecting individual phonons.
• The entire setup was maintained at an ultra-low temperature.
• Phonons used in the study had frequencies too high for human hearing and represented the collective vibration of around one quadrillion atoms.
• Phonons interacted with the comb-like low photons interacting with an optical beam splitter.
• A phonon emitted from one side of the channel was refreshed.
• A phonon emitted from one side of the channel was reflected 50% of the time and transmitted to the other the remaining 50%.
• Simultaneously emitted phonons from both sides both ended up on the one, confirming expectations.