Implementation of QKD BB84

Summary

The video script delves into the implementation of the BB8 protocol for quantum key distribution (QKD), which utilizes the polarization of single photons to encode key bits. It explains the rectilinear and diagonal bases and their respective polarizations. The script outlines the process of QKD, from Alice's random bit string generation to Bob's secure photon measurements, and the subsequent key extraction. It also discusses the security aspect by illustrating how an eavesdropper, Eve, introduces discrepancies by measuring and retransmitting photons, which can be detected by Alice and Bob. The use of Q-Scape simulations on the IBM platform with poly Xcode and Hadamard gates is highlighted to demonstrate the quantum circuit's functionality and security.

Takeaways

• 🔐 Quantum Key Distribution (QKD) BB-8 is the first protocol for secure communication using the polarization state of single photons.
• 🌟 The BB-8 protocol utilizes two bases for encoding: rectilinear (0-degree horizontal and 90-degree vertical polarization) and diagonal (45-degree diagonal and 135-degree anti-diagonal polarization).
• 🛰️ The four possible quantum states for encoding bits are 0, 1, +1, and -1, derived from the two bases.
• 💡 QKD BB-8 is simulated using Q-Scape simulations on the IBM platform, with gates like the Pauli-X gate for bit value creation and the Hadamard gate for superposition.
• 🔬 The security of the key exchange is verified by measuring and comparing the bases; if they match, the exchange is secure.
• 👤 The implementation of BB-8 requires a team consisting of Alice (sender), Bob (receiver), an authenticated public classical channel, and a potentially insecure private quantum channel.
• 🔄 Alice generates a random bit string and encodes it using photons with random polarization from the four possibilities.
• 🔍 Bob randomly decides the measurement basis for each photon and records the results, only announcing his choice of measurement bases through the classical channel.
• 🕵️‍♀️ Eavesdropper Eve's presence is detected if there is inconsistency in the measurement results and the agreed-upon bases between Alice and Bob.
• 🔄 The key is obtained by Alice and Bob agreeing on the measurement results for more than 25% of the bases and discarding the rest.
• 🚫 Eve cannot break the security of BB-8 as her measurements disturb the quantum system, leading to detectable discrepancies in the key exchange.

Q & A

What is the BB8 protocol?

The BB8 protocol is the first quantum key distribution protocol, which uses the polarization state of single photons to encode key bits for secure communication.

What are the two bases used to represent a bit in BB8 protocol?

The two bases used are the rectilinear basis, which consists of 0-degree horizontal and 90-degree vertical polarization, and the diagonal basis, which consists of 45-degree diagonal and 135-degree anti-diagonal polarization.

What are the four possible quantum states in the BB8 protocol?

The four possible quantum states are 0 and 1 from the rectilinear basis, and plus and minus from the diagonal basis.

How does one access the quantum computer for BB8 simulations?

The BB8 simulations are accessed using Q-Scape simulations on the IBM platform.

What are the two main gates used in the BB8 simulation?

The two main gates used are the Pauli-X gate, which allows the conversion of the state of the qubit, and the Hadamard gate, which creates a superposition of 0 and 1.

What does the histogram in the BB8 simulation represent?

The histogram represents the probability of Alice and Bob having the same qubits, indicating a secure key exchange, or Bob receiving different qubits from Alice, indicating a potential eavesdropper.

How does the BB8 protocol ensure the detection of an eavesdropper?

By comparing the bases used for encoding and measurement, if there is an inconsistency or disagreement, it suggests that an eavesdropper has tampered with the key exchange.

What are the roles of Alice and Bob in the BB8 protocol?

Alice is the sender who chooses a random bit string and encodes it using photon polarization. Bob is the receiver who measures the photons in randomly chosen bases and communicates with Alice through a classical channel.

What is the purpose of the authenticated public classical channel in the BB8 protocol?

The authenticated public classical channel is required for Alice and Bob to securely exchange information about their chosen measurement bases without the risk of tampering.

How does the BB8 protocol handle the presence of an eavesdropper?

The BB8 protocol assumes an eavesdropper may intercept and measure the photons. However, due to the nature of quantum measurement, any attempt to measure will disturb the system, leading to detectable discrepancies in the key exchange between Alice and Bob.

What is the process for Alice and Bob to obtain the final key in the BB8 protocol?

Alice and Bob first discard bits where their chosen bases do not match. Then, they discuss a subset of the remaining bits to check for eavesdropping. If no discrepancies are found, the remaining bits become the final key.