Quantum Tunneling: Crossing Impossible Barriers

Mihirsinh Chauhan
4 min readSep 7, 2023


Welcome to Day 7 of your quantum exploration journey. Today, we’re delving into the extraordinary phenomenon of quantum tunneling. This quantum effect allows particles to overcome seemingly insurmountable barriers, defying classical physics and opening up a world of intriguing possibilities.

Quantum Tunneling: Breaking Through Barriers

In classical physics, we often think of particles as having definite positions and energies. However, in the quantum world, particles are described by wave functions, which give us a probability distribution of where the particle is likely to be found. Quantum tunneling arises when a particle, described by a wave function, has a finite probability of “tunneling” through a barrier, even when its energy is less than the barrier’s height.

Key Concepts in Quantum Tunneling:

  1. Barrier Potential: Imagine a particle encountering a potential energy barrier, like a hill or a wall. In classical physics, if the particle’s energy is lower than the height of the barrier, it cannot cross it. However, in quantum mechanics, the particle can still penetrate the barrier.
  2. Wave Function: The wave function of a particle represents the probability distribution of finding the particle at different positions. It describes the particle as a wave of probabilities rather than a definite point-like object.
  3. Wave Function Penetration: When a particle’s wave function encounters a barrier, there is a probability that the wave function extends into the barrier region. This means there is a chance the particle can be found on the other side of the barrier, even when classical physics would suggest it’s impossible.
  4. Exponential Decay: The probability of tunneling decreases exponentially with the width and height of the barrier. However, it is never zero, no matter how high or thick the barrier is.

Mathematical Representation:

The probability of quantum tunneling can be mathematically expressed using the Schrödinger equation and the wave function. It involves solving the Schrödinger equation for a particle encountering a potential barrier.

The Schrödinger equation for a non-relativistic particle in one dimension is given by

Quantum Tunneling Probability:

To describe quantum tunneling mathematically, we consider a scenario where a particle encounters a potential barrier. Let’s denote the potential energy as V(x), where V(x)>0 within the barrier region and V(x)=0 outside the barrier.

The probability of finding the particle on the other side of the barrier can be calculated using the transmission coefficient (T):

Here’s what these terms represent:

  • T is the transmission coefficient, which represents the probability that the particle tunnels through the barrier.
  • κ is the wave vector inside the barrier and is related to the energy of the particle and the height and shape of the barrier.
  • a is the width of the barrier, which is the distance the particle must tunnel through.
  • The exponential term quantifies how rapidly the probability of tunneling decreases with increasing barrier width (a) and increasing barrier height V(x).

In general, as the barrier becomes wider or taller, the transmission probability (T) decreases exponentially. However, it’s important to note that it never becomes zero. There is always a finite probability of tunneling, even through seemingly impenetrable barriers.

This mathematical representation underscores the probabilistic and wave-like nature of quantum tunneling, where particles can exhibit behavior that defies classical expectations and penetrate energy barriers, albeit with reduced probability as the barriers become more formidable.

Applications and Implications:

Quantum tunneling has profound implications and applications in various fields:

  • Electronics: It is crucial for the operation of transistors and the phenomenon of quantum-dot cellular automata in microelectronics.
  • Nuclear Fusion: Quantum tunneling plays a role in nuclear fusion processes in stars and in experimental fusion reactors.
  • Chemistry: Understanding tunneling helps explain chemical reactions, particularly in enzymatic reactions in biochemistry.
  • Quantum Computing: Quantum tunneling is leveraged in quantum algorithms, such as quantum annealing, to find solutions to complex optimization problems.
  • Scanning Tunneling Microscopy: It is used in nanotechnology tools like scanning tunneling microscopes to image and manipulate individual atoms and molecules on surfaces.


In Day 7, we’ve explored the intriguing concept of quantum tunneling, where particles can overcome energy barriers that would be insurmountable in classical physics. This phenomenon challenges our classical intuitions and has far-reaching implications, from electronics and chemistry to quantum computing and beyond. Quantum tunneling is a testament to the remarkable and often counterintuitive nature of the quantum world.

#Day7 of #Quantum30 day challenge



Mihirsinh Chauhan

《Quantum computing Enthusiast |Future Innovator》《Under grad at SVNIT | ML| Buisness Amateur》