** ARCHIVES**

*Syllabus*

*GS-3: Science and Technology- developments and their applications and effects in everyday life.*
*GS-3: Awareness in the fields of IT, Space, Computers, robotics*

**Context**: The allure of quantum computers (QC) is their ability to take advantage of quantum physics to solve problems too complex for computers that use classical physics.

- The 2022 Nobel Prize for physics was awarded for work that rigorously tested one such ‘experience’ and paved the way for its applications in computing – which speaks to the contemporary importance of QCs
- In 2021 alone, the Indian government launched a National Mission to study quantum technologies with an allocation of ₹8,000 crore; the army opened a quantum research facility in Madhya Pradesh; and the Department of Science and Technology co-launched another facility in Pune.
- Given the wide range of applications, understanding what QCs really is crucial to sidestep the misinformation surrounding it and develop expectations that are closer to reality.

**How does a computer use physics? **** **

- A macroscopic object – like a ball, a chair or a person – can be at
**only one location at a time**; this location **can be predicted accurately**; and the object’s effects on its surroundings can’t be transmitted faster than at the speed of light. This is the classical ‘experience’ of reality.
- For example, you can observe a ball flying through the air and plot its trajectory according to Newton’s laws. 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. In this realm, **you can’t pinpoint the location of an electron**.
- You can only know that it will be present in a given volume of space, with a probability attached to each point in the volume – like 10% at point A and 5% at point B. When you probe this volume in a stronger way, you might find the electron at point B. If you repeatedly probe this volume, you will find the electron at point B 5% of the time.
- There are many interpretations of the laws of quantum physics. One is the
**‘Copenhagen interpretation’,** which Erwin Schrödinger popularised using a thought-experiment he devised in 1935.
- There is a cat in a closed box with a bowl of poison. There is no way to 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 and dead**.
- When you open the box, you force the superposition to collapse to a single state. The state to which it collapses depends on the probability of each state.
- Similarly, when you probe the volume, you
**force the superposition of the electrons’ states to collapse to one** depending on the probability of each state.

- The other ‘experience’ relevant to quantum-computing is
**entanglement**. When two particles are entangled and then separated by an arbitrary distance (even more than 1,000 km), making an observation on one particle, and thus causing its superposition to collapse, will instantaneously cause the superposition of the other particle to collapse as well.
- This phenomenon seems to violate the notion that the speed of light is the universe’s ultimate speed limit.
- That is, the second particle’s superposition will collapse to a single state in
**less than three hundredths of a second**, which is the time light takes to travel 1,000 km.

**How would a computer use superposition? **** **

- The bit is the fundamental unit of a classical computer. Its value is 1 if a corresponding transistor is on and 0 if the transistor is off.
- The transistor can be in one of two states at a time – on or off – so a bit can have one of two values at a time, 0 or 1.
- The
**qubit** is the fundamental unit of a Quantum Computing. It’s typically a particle like an electron.
- Google and IBM have been known to use transmons, where pairs of bound electrons oscillate between two superconductors to designate the two states.

- Some information is directly encoded on the qubit: if the spin of an electron is pointing up, it means 1; when 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 a third kind of state.
- The
**qubits are entangled** to ensure they work together. If one qubit is probed to reveal its state, so will some of or all the other qubits, depending on the calculation being performed. The computer’s final output is the state to which all the qubits have collapsed.
- One qubit can encode two states. Five qubits can encode 32 states. A computer with N qubits can encode 2
^{N} states – whereas a computer with N transistors can only encode 2 × N states.
- So a qubit-based computer can access more states than a transistor-based computer, and thus access
**more computational pathways** and solutions to more complex problems.

**How has Quantum Mechanics evolved over a period of time?**

- It was developed in the early 20th century to
**describe nature in the small** — at the scale of atoms and elementary particles.
- It helped in understanding of the physical world, including the interaction of light and matter and on subjects such as gravity and black holes.
- It led to ubiquitous
**inventions such as lasers and semiconductor transistors**
- A
**second revolution** is currently under way with the goal of controlling and harnessing the properties of quantum mechanics.
**Recent Developments:**

**How come we’re not using Quantum Computers?**** **

- A practical QC needs at least 1,000 qubits. The current biggest quantum processor has 433 qubits. There are no theoretical limits on larger processors; the
**barrier is engineering-related.**
**Technical Difficulties:** The challenge lies in harnessing the properties of quantum superposition and entanglement in a highly controlled manner by building a system composed of carefully designed building blocks called quantum bits or qubits.
- Qubits exist in superposition in specific conditions, including very low temperature (~0.01 K), with radiation-shielding and protection against physical shock.

**Fragility of Qubits:** The qubits tend to be very fragile and lose their “quantumness” if not controlled properly, and a careful choice of materials, design and engineering is required to get them to work.
- Tap your finger on the table and the states of the qubit sitting on it could collapse.
- Material or electromagnetic defects in the circuitry between qubits could also ‘corrupt’ their states and bias the eventual result.
- Researchers are yet to build QCs that completely
**eliminate these disturbances in systems **with a few dozen qubits.

**Theoritical Challenges** of creating the algorithms and applications for quantum computers
- Researchers are also yet to build
**QCs that don’t amplify errors** when more qubits are added. This challenge is related to a fundamental problem: unless the rate of errors is kept under a certain threshold, more qubits will only increase the informational noise.
- Practical QCs will require at least lakhs of qubits, operating with superconducting circuits that we’re yet to build – apart from other components like the firmware, circuit optimisation, 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 speculative profits, while companies that promise developers access to quantum circuits on the cloud often offer physical qubits with noticeable error rates.

**What is India’s National Mission on Quantum Technologies & Applications (NM-QTA)?**** **

- The mission will oversee the development of quantum technologies for communications, computing, materials development and cryptography.
- The mission addresses the constraints (listed above) that led to slow progression of country in quantum field, through adoption of holistic approach.
- Announced in Budget 2020
- Period: Five years (2020-25)
- Total Funds: Rs 8000 years
- Implementing Body: Department of Science & Technology (DST)

**Significance of the mission:**

- The mission may eventually lead to the creation of a
**super-secure communication network **
- It will help prepare next generation
**skilled manpower**, boost translational research and also encourage entrepreneurship and start-up ecosystem development.
- It will find utility in finding
**solution for complex problems** in fields of computing, communications, sensing, chemistry, cryptography, imaging and mechanic
- The mission will enable
**India to emerge as Global leader** in the field through increased investment & focus in Quantum Technologies

**Main Practice Question: What is Quantum Computing and why we are not yet having Quantum Computers at home replacing classical computers?**

**Note:** Write answer his question in the comment section.