Quantum Physics & Computing : Part 2

THE MAGIC BEHIND QUANTUM COMPUTERS

Quantum Gates: The Building Blocks

Think about a classical computer first. It works like a factory with tiny workers with instructions called logic gates (AND, OR, NOT). Each gate makes a decision with 0s and 1s — for example:

• AND: Both switches ON → light ON. Otherwise, OFF.
• OR: One switch is ON -> the other switch is OFF
• NOT: If switch is ON → turn it OFF. If it’s OFF → turn it ON.

That’s how all your apps, games, and browsers work — by combining billions of these gates.

Enter the Quantum World

In a quantum computer, the workers are not classical gates, but quantum gates. Instead of flipping simple 0s and 1s, they manipulate qubits (quantum bits) — which can be 0, 1, or both at the same time (superposition).

Think of quantum gates as dance moves:

• Every move shifts the dancer (the qubit) into a new style, pose, or direction.
• By combining different dance steps (gates), you choreograph an entire performance (the quantum algorithm).

The Main Quantum Gates

1. Hadamard Gate (H) :  Puts a qubit into superposition — making it a mix of 0 and 1 Imagine tossing a coin. Before it lands, it is both heads and tails at once. That is what Hadamard does to a qubit. Use: It is the starting move for most quantum algorithms.
2. Pauli-X Gate (NOT Gate in Quantum): Flips the state of a qubit. If it is 0, it becomes 1. If it is 1, it becomes 0. Like turning a light switch ON if it is OFF, or OFF if it is ON. Use: Basic flipping, like the NOT gate in classical computers.
3. CNOT Gate (Controlled-NOT):  A two-qubit gate. If the first qubit (control) is 1, the second qubit (target) flips. If control is 0, the target stays the same. Imagine two dancers. The second dancer only changes their move if the first dancer lifts their hand. Use: Creates entanglement, one of the most powerful features in quantum computing.

Interference in Quantum Computing

Think about water waves.

• When two waves meet, they can add up (becoming a bigger wave) or cancel each other out (flattening the water).
• This is called interference.

Now imagine your qubits (quantum bits) behaving like waves instead of regular bits. Their "wave-like nature" lets us control probabilities of outcomes by letting their paths interfere with each other.

In Quantum Computing

• A qubit can be in a superposition of states (both 0 and 1 at once).
• When you apply quantum gates, you are basically adjusting the "waves" of probabilities.
• By carefully designing circuits, quantum algorithms amplify the probability of correct answers (constructive interference) and reduce the wrong ones (destructive interference).

This is the secret sauce of why quantum computers can solve some problems faster.

In short: Interference in quantum computing is about making the right answers louder and the wrong answers quieter by playing with qubit waves.

How does a Quantum Computer Looks like?

• A quantum computer doesn’t look like a laptop or desktop.
• Instead, it often looks like a giant chandelier or a golden octopus hanging from the ceiling.
• Why? Because qubits (the heart of a quantum computer) are extremely delicate. They need to be kept at ultra-cold temperatures — colder than outer space!

Core Parts of a Quantum Computer

Qubits—the information carriers—are extremely delicate. Heat, vibration, stray magnetic fields, even a single photon of the wrong kind can ruin a calculation. So the machine needs:

• A quantum chip (the “brain”): Superconducting circuits, ions, atoms, photons, or spins in diamond/silicon. Stores and manipulates qubits (0, 1, or both at once).
• A dilution refrigerator (for superconducting chips): A super-freezer that cools the chip to about 10–15 millikelvin (that’s ~-273°C), colder than outer space. Built in layers (“stages”) that get progressively colder: ~50 K → 4 K → 0.1 K → 0.01 K.
• Control & readout electronics (the conductor): Room-temperature racks with signal generators, waveform generators, and fast digitizers. Microwave pulses or laser beams tell qubits what gate to perform. Cryogenic amplifiers and filters carry faint signals back from the chip to be measured.
• Isolation (the quiet bubble): Magnetic shields, vibration isolation, and vacuum keep noise out. For ions/atoms: ultra-high vacuum and laser cooling keep particles perfectly still.
• A classical computer : You write code on a normal computer. It compiles to “pulse instructions,” sends them to the quantum hardware, then collects and processes the results.

Does It Look Like a Laptop or Desktop?

• No. A quantum computer is usually a big room-sized machine.
• The actual quantum chip (where qubits live) is very small — often smaller than a coin.
• But the support system (cooling, shielding, controls) is HUGE.

Imagine:

• The quantum chip = the tiny heart.
• The machine around it = life-support system keeping it alive.

Example: IBM’s Quantum Computer

• IBM’s quantum computers are stored in giant golden, chandelier-like machines.
• The chip with qubits is at the bottom of the chandelier, deep inside the refrigerator.
• The golden wires carry signals to and from the qubits.

In short:

• A quantum computer is not a sleek laptop.
• It’s more like a giant scientific lab setup with a tiny chip at its heart.
• The magic is in that chip, but the massive structure around it keeps it alive and working.

1. IBM Quantum Computer: https://www.ibm.com/quantum
2. Microsoft's Quantum Chip : Majorana 1 https://news.microsoft.com/azure-quantum/

That is all for now. I will try to cover "How Quantum Computers Solve Problems" in the next Part.