QUANTUM PHYSICS

1. Context

2. Quantum Physics

• A macroscopic object-like a ball, chair, or a person- can be at only one location at a time, which can be predicted accurately; and the object's effects on its surrounding can't be transmitted faster than at the speed of light. This is the classical 'experience' of reality.
• Observe a ball flying through the air and plot its path. You can predict exactly where the ball will be at a given time. If the ball strikes the ground, you will see it doing so in the time it takes light to travel through the atmosphere to you.
• Quantum physics describes reality at the subatomic scale, where the objects are particles like electrons. Here you can't pinpoint the location of an electron. You can only know that it will be present in some volume of space, with a probability attached to each point in the volume: say 10% at point A and 5% at point B.
• You might find the electron at point B when you probe the volume. If you repeatedly probe the volume, you will find the electron at point B 5% of the time.
• Ewin Schrodinger described one interpretation of the laws of quantum physics in a famous thought experiment in 1935. There's a cat in a closed box with a bowl of poison. You can't know whether the cat is alive or dead without opening the box. 
• In this time, the cat is said to exist in a superposition of two states: alive or dead. When you open the box, you force the superstition to collapse into a single state. The state to which it collapses depends on the probability of each state. The same thing happens with the electron's locations.

3. Bits

3.1 Quantum bits(qubits)

• In quantum computing, a qubit or quantum bit is the basic unit of quantum information- the quantum version of the classical binary bit physically realized with a two-state device. A qubit is a two-state quantum-mechanical system, one of the simplest quantum systems displaying the peculiarity of quantum mechanics.
• The qubit is the fundamental unit of QC. It could be a particle like an electron. Some information is directly encoded on the qubit: if the electron's spin is pointing up, it means 1; if the spin is pointing down, it means 0. But instead of being either 1 or 0, the information is encoded in a superposition: say, 45% 0 plus 55% 1.
• This is entirely unlike the two separate states of 0 and 1 and is the third kind of state.

4. What is quantum superposition?

• Quantum superposition is the theory that sub-atomic particles exist in multiple states simultaneously.
• The practical application of this mind-bending version of reality is most obvious in quantum computers. While digital computers store data as bits (the ones and zeros of binary), quantum computers use qubits that exist as a one, zero, or both at the same time.
• This superposition state creates a practically infinite range of possibilities, allowing for incredibly fast simultaneous and parallel calculations.

5. Challenges

5.1 Security-related issues

• Quantum computing can have a disruptive effect on cryptographic encryption, which secures communications and computers.
• It might pose a challenge for the government also because if this technology goes into the wrong hands, all the government's official and confidential data will be at risk of being hacked and misused.

5.2 Technological Issues

• The challenge lies in harnessing the properties of quantum superposition in a highly controlled manner. The qubits tend to be very fragile and lose their "quantumness" if not controlled properly. Also, a careful choice of materials, design, and engineering is required to get them to work.
• On the theoretical front lies the challenge of creating algorithms and applications for quantum computers.

5.3 Other Challenges

• Practical QCs will require at least lakhs of qubits, operating with superconducting circuits that we are yet to build apart from other components like firmware, circuit optimization, compilers, and algorithms that make use of quantum physics possibilities. Quantum supremacy itself- a QC doing something a classical computer can't-is thus at least decades away.
• The billions being invested in this technology today are based on speculation profits, while companies that promise developers access to quantum circuits on the cloud often offer physical qubits with noticeable error rates. 

For Mains