quantum computing with photons

 demo : https://www.youtube.com/watch?v=t25UzI61NCA

1. Why Photons for Quantum Computing

  • Photons do not interact much with the environment, so they are less noisy.

  • They can be controlled at room temperature.

  • Optical components (mirrors, beam splitters, wave plates) are easily available.

  • Photons are easy to generate and detect compared to many other quantum systems.

2. Why the 6-Qubit Photonic Quantum Computer Is Special

  • Photons do not interact with each other, making gate operations difficult.

  • Most photonic systems are probabilistic (success < 100%).

  • IISc’s 6-qubit system is fully deterministic (100% success).

  • Only 2 photons were used.

  • Multiple degrees of freedom of photons were used to create 6 qubits.

  • Gate operations were demonstrated efficiently.

3. Major Challenge in Photonic Quantum Computing

  • Photon–photon interaction is weak → hard to create gates.

  • Alignment of optical components requires nanometer/micrometer precision.

  • Bulk optical setups are hard to scale.

  • Scaling beyond 6 qubits may again introduce probabilistic behavior.

4. Future Direction / Scalability

  • Move from bulk optics to integrated photonic circuits.

  • Use waveguides to reduce alignment issues.

  • Balance between deterministic and probabilistic schemes.

  • Miniaturization is key for real-world usage.

5. Skills Needed for Students (Career Guidance)

  • Strong foundation in optics (mirrors, lenses, focusing light).

  • Basic understanding of quantum mechanics.

  • Combination of optics + quantum mechanics → quantum optics.

  • Supporting skills are also important:

    • Electronics

    • Sensors

    • Detectors

    • Control systems

6. Unexpected Skill That Helped Prof. Chandrasekhar

  • He was trained as a theoretician, not an experimentalist.

  • Took a big risk moving from theory to experiments.

  • Willingness to fail and return to theory if needed.

  • Belief that theory and experiment must go together in quantum science.

7. Photons vs Students (Fun Question 😄)

  • Photons are easier to control because they follow mathematics.

  • Students have higher uncertainty—but that’s how they grow.

8. Work Style Insight

  • Research has no fixed timing (day/night).

  • Work continues until a problem is solved.

  • Passion defines work hours, not the clock.

9. Exams, Background & Confidence

  • Did not study in IIT/IISc for undergraduate.

  • Still competed globally and succeeded.

  • Key factors:

    • Hard work

    • Continuous learning

    • Taking chances

  • Institute name matters less than learning trajectory.

10. Distractions & Balance

  • Earlier generations had fewer distractions.

  • Today’s tools (AI, YouTube, social media) are not bad by default.

  • Important thing is how students use them productively.

  • Balance between work and hobbies improves creativity.

11. Key Quantum Mechanics Concepts Explained

  • Wave–particle duality: photons behave as both wave and particle.

  • Double-slit experiment proves this behavior.

  • Observation decides behavior:

    • Observed → particle

    • Not observed → wave

  • Information determines behavior.

12. Beam Splitter Experiments

  • A single photon never splits into two detections.

  • It chooses one detector → particle nature.

  • But interference patterns prove wave nature.

  • Photon takes both paths simultaneously until measured.

13. Qubits Explained Simply

  • Classical bit: only 0 or 1

  • Qubit: 0, 1, or both at the same time (superposition)

  • Implemented using:

    • Photon paths

    • Polarization (H/V)

    • Frequency

    • Other degrees of freedom

14. Core Resources of Quantum Computing

  1. Superposition

  2. Interference

  3. Entanglement

These three enable quantum advantage.

15. Entanglement

  • Two particles share a linked state.

  • Measuring one instantly defines the other.

  • Distance does not matter.

  • Powerful resource for computation and communication.

16. Quantum Gates

  • Bit flip

  • Hadamard (creates superposition)

  • Phase gate

  • Identity

  • Controlled-NOT (CNOT)

  • Universal gates are required to claim a quantum computer.

17. Measurement in Quantum Systems

  • Measurement collapses the state.

  • You cannot fully observe without disturbance.

  • Partial measurements give partial information.

  • Repeated measurements reconstruct information.

18. Classical vs Quantum Bits

ClassicalQuantum
Can be copiedCannot be copied
Measurement doesn’t change stateMeasurement collapses state
Can be erasedCannot be erased
DeterministicProbabilistic

19. Why Photons Are Advantageous

  • Long coherence time (less noise).

  • Room-temperature operation.

  • Multiple degrees of freedom per particle.

  • Fast processing.

20. Challenges with Photons

  • No natural interaction → hard gates.

  • Move at speed of light → timing is critical.

  • Scaling remains difficult.

21. Big Picture

  • Quantum technology is still very early-stage.

  • Next 10–20 years will define real applications.

  • Best time for students to enter the field is now.


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