Will ‘colour molecules’ make quantum computers accessible?
- February 27, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Will ‘colour molecules’ make quantum computers accessible?
Subject: Science and tech
Section: Awareness in IT and computer
Context:
- Many Physical systems qualify for qubits but most of them work at very low temperature.
- To overcome this researcher are working on alternative technologies to reduce cost and make quantum computers commercially feasible.
A classical computer:
- It is collection of information storage units (bits) has two states each, denoted 0 and 1.
- Any computation by computer is essentially result of the manipulation of the states of bits.
Quantum computers:
- A qubit is the fundamental physical component of a quantum computer.
- A qubit can exist in one of the two states (0 or 1) or unlike classical computers- a superposed state with contributions from both states.
Principle of Superposition:
- Superposed states (coherent superpositions) are important in quantum information-processing protocols.
- Superpositions are fragile due to interaction between the qubit and other systems.
- In more number of interaction channels, the superposition occurs faster and the qubit obtain one of the two states.
Problems in the process of quantum devices:
As a group of qubits are required to make a quantum device and thus qubits need to satisfy certain basic requirements:
the qubits should be identical but can’t be guaranteed due to manufacturing and some imperfections is possibility.
It should be relatively easy to integrate several qubits that can be operated controllably.
Overall the qubit system should be robust enough to function at room temperature without losing quantum features for reasonably long durations.
Available qubits :
- Many physical systems are suitable for realising qubits.Such options include superconducting junctions, trapped ions, and quantum dots. But these systems operate as qubits only at very low temperatures or in a high vacuum or both.
- In some cases low temperature is required for qubits to work while in others it is for superposition.
Commercial viability :
- Quantum computers based on such technologies are expensive that in long run will not be economically viable.
- Recently researchers in Japan, realised qubits at room temperature in a metal-organic framework (MOF).
Metal-Organic framework (MOF):
- A MOF is a network of repeated molecular arrangements.
- Repeating structure has a metal atom or ion with organic molecules attached to it.
- Each tentacle attaches to another metal atom, and the structure repeats itself to make up the MOF.
What are colour molecules and role of these in qubits devices:
- A chromophore is an organic molecule or a part of a larger molecule that absorbs light of some specific colour.
- An object containing such molecules thus appears to have some dominant colour.
- Since the presence of chromophores is responsible for the colouration, they are called “colour molecules”.
Example:
- The leaves of many plants appear green since the chromophore chlorophyll predominantly absorbs red and blue colours from sunlight.
Singlet :
- In lowest energy state (ground state) a chromophore molecule has a pair of electrons in a special configuration called a singlet.
- Every electron has inherent spin property. The spin of an electron points in two opposite directions having distinct quantum state.
Excited state:
- The chromophore molecule absorbs light and move to a higher energy level (i.e. an excited state).
- In a singlet, the spins of two electrons are in opposite directions.
- If two electrons, a lower energy and a higher energy, have spins in opposite directions, called as a singlet excited state.
- If the two electrons on different steps of the energy and have spin in same direction (say, +1 and +1), the configuration is triplet excited state.
Deexcitation:
- Release of extra energy by an excited molecular system
- is called deexcitation.
Singlet fission:
- Energy released in deexcitation of higher energy singlet excited state into a lower energy triplet excited state, excite a neighbouring chromophore molecule in a singlet ground state to jump to a triplet excited state.
- This generates two triplet excited chromophores from a singlet excited state chromophore is called singlet fission.
Singlet Induced Superposition:
- The very porous MOF networks allows the chromophores to rotate by a small degree and this rotation change the interaction strength between two adjacent chromophores.
- The interaction between the chromophores prepares the two pairs of electrons (in triplet state) in a superposition.
- The rotation-induced modulation ensures the long-lived superposition of triplet states by singlet fission.
Room temperature and very low temperature are necessary condition to long-lived coherence:
- According to Japanese team, even at room temperature, the coherence of the superposition of two four-electron states survived up to a fraction of a micro second (a long duration in the current context. This is a significant achievement.
- Other qubit systems require an extremely low temperature for coherence to last this long.