28 Feb Laser cooling of Positronium by CERN
This article covers ‘Daily Current Affairs’ and the topic details of ”Laser cooling of Positronium by CERN”.This topic is relevant in the “Science & Technology” section of the UPSC CSE exam.
Why in the News?
A multinational team of scientists has successfully demonstrated laser cooling of positronium for the very first time, marking a significant scientific milestone. The Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS) team at the European Organisation for Nuclear Research (CERN) conducted the ground-breaking experiment.
What is Positronium?
Positronium can be defined as a composite system comprising an electron and its corresponding antiparticle, the positron. Classified as an exotic atom or pseudo-atom, it mimics the behaviour of a hydrogen atom while possessing a reduced mass.
Properties of Positronium:
Positronium exists in two distinct forms known as ortho-positronium (o-Ps) and para-positronium (p-Ps), differentiated by their spin configurations.
- Spin States:
- Ortho-positronium: In this state, the spins of the electron and positron are parallel, resulting in a triplet state.
- Para-positronium: Here, the spins are anti-parallel, leading to a singlet state.
- Lifetime: The lifespan of positronium is notably brief, typically lasting on the order of nanoseconds, culminating in its annihilation.
- Annihilation: During the annihilation process, positronium emits two or three gamma-ray photons, each possessing an energy of 511 keV. This emission occurs as the entire rest of the energy of the electron-positron pair transforms into photons.
Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS)
- The Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEgIS) is a groundbreaking scientific initiative aimed at unravelling the mysteries surrounding antimatter and its interaction with gravity. Launched to explore the fundamental forces governing antimatter, AEgIS combines gravity measurements, interferometry techniques, and spectroscopy methods in a comprehensive approach.
- One of the primary objectives of the AEgIS experiment is to examine how antimatter, specifically antihydrogen, responds to gravitational forces. By subjecting antihydrogen atoms to precise gravitational measurements, scientists aim to gain insights into the gravitational behaviour of antimatter, a critical aspect of our understanding of the universe’s fundamental forces.
- Interferometry, a technique commonly employed in quantum physics, is a key component of AEgIS. This method involves combining and analysing multiple beams of antihydrogen particles to create interference patterns. The resulting interference fringes provide valuable data on the properties and behaviour of antihydrogen, offering a deeper understanding of antimatter physics.
- Spectroscopy, another integral aspect of the AEgIS experiment, involves the study of the interaction between antihydrogen and electromagnetic radiation. By analysing the spectral lines produced during these interactions, scientists can gather essential information about the energy levels and characteristics of antihydrogen atoms. This spectroscopic analysis contributes to refining our knowledge of the properties and dynamics of antimatter.
- The AEgIS experiment operates at the Antiproton Decelerator facility at CERN (European Organization for Nuclear Research). This cutting-edge facility allows scientists to produce and trap antihydrogen atoms, enabling meticulous experimentation and observation.
- The significance of AEgIS extends beyond the realm of antimatter physics. It plays a pivotal role in addressing fundamental questions about the symmetry between matter and antimatter, the nature of gravity’s influence on antimatter, and potential disparities in their behaviours.
About Laser Cooling
Laser cooling emerged as a revolutionary technique in the realms of atomic physics and quantum optics, showcasing the ability to decelerate and confine atomic and molecular particles. The core principle of this method lies in the interaction between light and charged matter, capitalising on the momentum transfer from photons to atoms.
Working Principle of Laser Cooling
- The mechanism hinges on the absorption and re-emission of photons. As an atom absorbs a photon, it ascends to a higher energy level, subsequently descending to a lower energy level upon re-emitting the photon. Laser cooling’s effectiveness lies in ensuring that the atom consistently re-emits the photon opposite to its motion. This meticulous process results in the atom losing more momentum to photons than it gains, leading to a gradual slowdown and eventual capture of atoms in optical traps.
- Typically employing a narrow-band laser with a confined frequency range, the AEgIS team has innovatively utilised a broad-band laser (~380 Kelvin to ~170 Kelvin) in their experiment. Employing a 70-nanosecond pulsed alexandrite-based laser system, this unconventional approach has facilitated the cooling of the positronium sample.
- Remarkably, the AEgIS experiment achieved successful laser cooling without the application of any external electric or magnetic field. This strategic simplification of the experimental setup not only showcases the versatility of laser cooling but also extends the positronium lifetime, opening new avenues for further exploration in quantum mechanics.
Significance of Laser Cooling
- Building blocks for antimatter research: Cooling antimatter lays the groundwork for creating antihydrogen and studying its behaviour in Earth’s gravity.
- Unveiling new frontiers: Laser cooling opens doors to creating a gamma-ray laser, potentially allowing us to peer into atomic nuclei and beyond.
- Deeper understanding of matter and antimatter: By meticulously controlling antimatter particles, scientists can probe their interactions with light, revealing the nature of our universe.
- Unlocking Bose-Einstein condensates and beyond: Laser cooling enables the creation of a positronium Bose-Einstein condensate, a unique state of matter with the potential for diverse applications. It includes the generation of a revolutionary gamma-ray laser.
- The groundwork for future discoveries: It facilitates the formation of ultracold antimatter systems and a degenerate gas of Positronium, crucial for advancing our understanding of the universe.
- Revolutionising antimatter research: High-precision manipulation allows detailed study of antimatter properties and behaviour, potentially revealing new physics.
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Prelims practice questions
Q1. What is the objective of laser cooling in the AEgIS experiment?
(a) Creating a Bose-Einstein condensate
(b) Analyzing dark matter
(c) Studying neutrinos
(d) Slowing down and trapping antihydrogen particles
Answer: d
Q2. What is the primary method used in laser cooling during the AEgIS experiment at CERN?
(a) Magnetic resonance
(b) Radiofrequency heating
(c) Absorption and re-emission of photons
(d) Gravitational acceleration
Answer: c
Mains practice question
Q1. Examine the properties of positronium, specifically ortho-positronium and para-positronium. How their spin configurations contribute to the overall behaviour of this exotic atom. How does the short lifespan of positronium play a role in its annihilation process?
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