**PHONONS**

**WHY IN NEWS ?**

- Recently, IBM published a paper in which it claimed to have demonstrated that a quantum computer could solve a useful problem that today’s conventional computers cannot.

**WHAT ARE QUANTUM COMPUTERS ?**

- A quantum computer is a computer that exploits quantum mechanical phenomena.
- At small scales, physical matter exhibits properties of both particles and waves, and quantum computing leverages this behavior using specialized hardware.
- Classical physics cannot explain the operation of these quantum devices.
- A scalable quantum computer could perform some calculations exponentially faster than any modern “classical” computer.
- Any computational problem that can be solved by a classical computer can also be solved by a quantum computer.

- Conversely, any problem that can be solved by a quantum computer can also be solved by a classical computer, at least in principle given enough time.
- In other words, quantum computers obey the Church–Turing thesis.
- This means that while quantum computers provide no additional advantages over classical computers in terms of computability, quantum algorithms for certain problems have significantly lower time complexities than corresponding known classical algorithms.
- Notably, quantum computers are believed to be able to solve many problems quickly that no classical computer could solve in any feasible amount of time—a feat known as “quantum supremacy.”

- The study of the computational complexity of problems with respect to quantum computers is known as quantum complexity theory.

**WHAT ARE QUBITS ?**

- Quantum computers use qubits as their basic units of information.
- A qubit can be a particle — like an electron; a collection of particles; or a quantum system engineered to behave like a particle.
- Particles can do funky things that large objects, like the semiconductors of classical computers, can’t because they are guided by the rules of quantum physics.
- For example, these rules allow each qubit to have the values ‘on’ and ‘off’ at the same time.
- The premise of quantum computing is that information can be ‘encoded’ in some property of the particle, like an electron’s spin, and then processed using these peculiar abilities.
- As a result, quantum computers are expected to perform complicated calculations that are out of reach of the best supercomputers of today.

**WHAT ARE PHONONS ?**

- Photons are packets of light energy; similarly, phonons are packets of vibrational energy.
- Phonons and electrons are the two main types of elementary particles or excitations in solids.
- Whereas electrons are responsible for the electrical properties of materials, phonons determine such things as the speed of sound within a material and how much heat it takes to change its temperature.
- Beamsplitters are used widely in optics research.
- Imagine a torchlight shining light along a straight line. This is basically a stream of photons.
- When a beamsplitter is placed in the light’s path, it will split the beam into two.
- While it seems simple, the working of a beamsplitter actually draws on quantum physics.
- We can then reflect these two beams to intersect each other, creating an interference pattern .
- However, researchers have found that an interference pattern appears even when they shine photons at the beamsplitter one by one.

### Types of Phonon:

When the unit cell consists of more than one atom, the crystal will contain two types of phonons. Thus, there are two types of phonons that we study in condensed matter physics:

- Acoustic Phonon: In acoustic phonons, both positive and negative ions swing together.
- Optical Phonon: In optical phonons, both positive and negative ions swing against each other. The optical phonons are excited easily by light.

**PROPERTIES OF PHONONS :**

- Phonons are often used as a quasiparticle, some popular research has shown that phonons and protons may indeed have some kind of mass and be affected by gravity.
- phonons are said to have a kind of negative mass and negative gravity.
- phonons are known to travel faster (with maximum velocity) in denser materials.
- It is projected that phonons would deflect away as it detects the difference in densities, exhibiting the qualities of a negative gravitational field.

**WAY FORWARD: PHONON-BASED COMPUTER :**

- The basic science question is whether phonons … actually behave the way quantum mechanics says they should,” Andrew Cleland, a physicist at the Pritzker School of Molecular Engineering and a member of the study team, told Physics magazine.
- His team’s tests proved that they do.
- But it’s still a long way from here to a functional quantum computer that uses phonons as units of information.

**SYLLABUS:** MAINS, GS-3, SCIENCE AND TECHNOLOGY

**WAY FORWARD:** THE HINDU