Implementation of QKD BB84
Summary
TLDRThe 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.
Outlines
🔐 Introduction to Quantum Key Distribution with BB8-4 Protocol
This paragraph introduces the BB8-4 protocol, the first quantum key distribution method, which utilizes the polarization state of single photons to encode key bits. The key bits can be represented using two bases: rectilinear (0-degree horizontal and 90-degree vertical polarization) and diagonal (45-degree and 135-degree polarization). The speaker explains how they accessed a quantum computer via Q-Scape simulations on the IBM platform, using specific quantum gates like the poly Xcode and Hadamard gate to manipulate qubits. The simulation circuit is described, highlighting the process of encoding and measuring qubits to ensure a secure key exchange between Alice and Bob. The presence of an eavesdropper, Eve, is also discussed, with the simulation showing how her interference can be detected, thus proving the security of the BB8-4 protocol.
🕵️♀️ Eavesdropping Detection in Quantum Key Distribution
The second paragraph delves into the scenario where an eavesdropper, Eve, attempts to intercept the quantum communication between Alice and Bob. It outlines the steps taken by Alice to generate and send photons with random polarization, and how Eve's interception and measurement of these photons in randomly chosen bases inevitably disturbs the quantum system. This disturbance results in discrepancies when Bob measures the photons, which he receives from Eve rather than directly from Alice. The protocol involves Alice and Bob comparing their measurement bases through a classical channel, discarding bits where the bases do not match, and then checking a subset of the remaining bits to detect any inconsistencies caused by eavesdropping. The paragraph concludes by emphasizing that Eve's actions, while potentially allowing her to learn some information, also introduce detectable errors, thus maintaining the security of the quantum key distribution process.
Mindmap
Keywords
💡Quantum Key Distribution
💡Polarization State
💡Q-Scape Simulations
💡Pauli-X Gate
💡Hadamard Gate
💡Alice
💡Bob
💡Eve
💡Rectilinear Basis
💡Diagonal Basis
💡Measurement
Highlights
Introduction of the BB8 protocol, the first quantum key distribution protocol.
Use of the polarization state of single photons to encode key bits.
Two bases for bit representation: rectilinear and diagonal.
Four possible quantum states for encoding bits: 0, 1, +, -.
Accessing a quantum computer through Q-Scape simulations on the IBM platform.
Use of the Pauli-X gate for state conversion and the Hadamard gate for superposition.
Simulation circuit without Eve, using five bits and key exchange security.
Histogram showing Alice and Bob having the same qubits with a probability of 1.
Simulation with Eve, demonstrating the detection of eavesdropping.
Requirement of an authenticated public classical channel between Alice and Bob.
Role of Alice as the sender and Bob as the receiver in the quantum key distribution.
Process of Alice choosing a random bit string and photon polarization.
Bob's random choice of measurement basis for each photon.
Special properties of the rectilinear and diagonal bases in information loss.
Bob's method of obtaining meaningful data from half the photons detected.
Process of Alice and Bob comparing bases and discarding mismatches.
Verification of measurement results and formation of the key.
Introduction of Eve as an eavesdropper intercepting Alice's photons.
Eve's impact on the system by measuring and retransmitting photons.
Detection of eavesdropping through inconsistencies in measurement results.
Eve's inability to break the security of the BB8 protocol.
Conclusion on the security of the BB8 quantum key distribution protocol.
Transcripts
hello everyone today I'm going to
introduce you to my topic that is
implementation of quantum key
distribution
bb-8 for bb-8 for is the first quantum
key distribution protocol and it uses
the polarization state of single photons
to encode the key bits therefore a bit
can be represented by polarizing the
photon in either of the two bases first
rectilinear basal which consists of 0
degree horizontal and 90 degree vertical
polarization second diagonal basis which
consists of 45 degree diagonal and 135
degree anti-diagonal polarization the
four possible quantum states are 0 1
from the rectilinear basis plus minus
from the diagonal basis how to access
the quantum computer I did this by using
Q scape simulations on IBM platform
there are two main gates used for the
simulation first is the poly Xcode which
allows to convert the state of the qubit
and the other is the high Hadamard gate
which allows to create a superposition
of 0 and 1 this is my circuit for the
simulation without Eve with five of bits
where I apply the x-naught gate to
create the bit value 1 and Hadamard gate
to create superpositions whenever
diagonal basis is chosen measurement and
comparing the basis tells if the key
exchange is secure the histogram
represents that Alice and Bob have the
same qubits with probability equal to 1
similarly this is my circuit for the
simulation of the circuit with 5 bits
kiss-kiss circuit with Eve measurement
and comparing the basis tells if the key
exchange has been tampered the histogram
represents that the qubits received by
Bob are not the same sent by Alice with
the probability of 1
my result is that if comparison of bases
agree and alison bob find no
inconsistency eavesdropper can be
detected thus bd8 phone is secure now
the question is who and what do we need
for this implementation so let's meet
the team firstly there is alice the
sender then there is bob the receiver an
authenticated public classical channel
between them is required which means
that all the information exchanged using
this channel is secured a private
quantum Channel which may not be secure
and following other steps step one Alice
chooses a random bit string step 2 to
create a photon Alice randomly chooses a
polarization from the four possibilities
and so her photons look like this then
using the quantum Channel Alice sends
the string of photons to Bob Bob decides
randomly for each photon whether to
measure the photon in rectilinear
polarization or its diagonally
realization what is so special about
these bases all information is lost when
one attempts to measure the rectilinear
polarization of a diagonal photon or
vice versa if Alice sends 0 or 1 and Bob
happens to choose the rectilinear basis
then his measurement will pick out the
correct state and his bit assignment
will exactly match the one Alice sent
but if he chooses the rectilinear basis
for a photon plus or minus then a
measurement on plus and minus will yield
0 or 1 with equal probability
due to the rectilinear basis similarly
if the diagonal basis is used for 0 or 1
the result will be random
Bob obtains meaningful data from only
half the photons he detects those for
which he guessed the correct
polarization basis
for each bit Bob records the results of
the measurements but keeps them secret
Bob announces to the classical channel
only his choice of measurement bases
alice compares the bases announced by
Bob with bases chosen by her and answers
of the encoding bases and a measurement
bases agree for each bit they discard
the positions that do not have the same
bases chosen by both of them then they
discuss the positions of more than 25%
of the bases from the correct bases to
check the measurement results and the
measurement result is verified for those
bases the other results from the correct
bases become the key and this is how the
key is obtained now we have an
additional person in the system Eve the
eavesdropper who wants to intercept the
information shared by Alice and Bob we
assume an attack that Eve intercepts
Alice photons measures them in randomly
chosen bases and forward the photons to
Bob now we will see how it will affect
the system step 1
Alice chooses a random bit string step 2
for each photon Alice randomly chooses
the polarization from the four
possibilities and this is how Alice
photons will look like but before Alice
could send these photons to Bob Eve
intercepts the photons Eve decides
randomly for each photon whether to
measure the photons rectilinear or
diagonally pollenization but the act of
measuring a quantum system disturbs the
system and because of the wrong
prediction of some bases Eve could not
produce the exact same photons as Alice
to send to Bob and therefore Eve sends
his version of Alice photons to Bob Bob
decides randomly for each photo
whether to measure the photons
rectilinear or diagonally ization for
each bit Bob records the results of the
measurements but keeps them secret and
through the classical channel only his
choicest measurement bases as he would
do if he was not present is announced
eve has full access to the announced
information on the classical channel but
she can only listen and cannot tamper
with the signals alice compares the
basis announced by Bob with the basis
chosen by her Alice answers if the
encoding basis and the measurement basis
agree for each bit they discard the bit
positions that do not have the same
basis chosen by both of them then they
discuss the positions of more than 25%
of the basis from the correct basis to
check the measurement results due to the
eats interception the measurement
results are not correct and this is how
eavesdropping is detected so can Eve
brings the security and the answer is if
it decides to measure and retransmit all
the photons which intercepts she may
learn the correct polarization for half
of the photons but at the same time this
action of force induces a disagreement
to about 1/4 of the photons which Bob
may measure during using direct basis
thus if cannot break the security thank
you
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