Enter the Future of Communication with Quantum Mechanics
By Christopher Pinkston
A quantum (plural: quanta) is the smallest discrete unit of a phenomenon. For example, a quantum of light is a photon, and a quantum of electricity is an electron. Quantum comes from Latin, meaning "an amount" or "how much?" If something is quantifiable, then it can be measured.
History of Quantum Mechanics
Planck's Quantum Hypothesis (1900): Max Planck proposed the idea
that energy is quantized, leading to the birth of quantum theory.
He introduced the concept of quanta, discrete packets of energy.
Einstein's Photoelectric Effect (1905): Albert Einstein explained
the photoelectric effect by proposing that light consists of
quanta of energy called photons, further solidifying the concept
of quantization.
Bohr's Model of the Atom (1913): Niels Bohr developed a quantum
model of the atom, which incorporated quantized electron orbits
and explained atomic spectra.
Schrodinger's Wave Equation (1926): Erwin Schrödinger formulated
the wave equation, which describes the behavior of quantum
mechanical systems in terms of wave functions.
Heisenberg's Uncertainty Principle (1927): Werner Heisenberg
introduced the uncertainty principle, stating that there is a
fundamental limit to the precision with which certain pairs of
complementary variables, such as position and momentum, can be
known simultaneously.
Dirac's Relativistic Quantum Mechanics (1928): Paul Dirac
developed relativistic quantum mechanics, which extended quantum
theory to incorporate Einstein's theory of relativity.
Bell's Theorem (1964): John Bell proposed Bell's Theorem, which
experimentally tested the predictions of quantum mechanics against
Einstein's preferred local hidden variable theories. The
experiments supported quantum mechanics, showing that quantum
entanglement did indeed work as predicted, even over large
distances.
Principles of Quantum Mechanics
Quantum Superposition: In classical computing, a bit can be either
0 or 1. In quantum computing, a qubit (quantum bit) can exist in a
superposition of both states simultaneously.
Quantum Entanglement: Quantum entanglement occurs when two or more
particles become correlated in such a way that the state of one
particle instantaneously affects the state of the other(s),
regardless of the distance between them. This phenomenon enables
the creation of secure encryption keys and the transmission of
information in a highly secure manner.
Quantum Uncertainty: Heisenberg's Uncertainty Principle states
that certain pairs of physical properties, such as position and
momentum, cannot be simultaneously measured with arbitrary
precision.
Quantum Key Distribution (QKD)
Quantum key distribution (QKD) protocols utilize entangled
particles to ensure that any attempt at intercepting the
communication would be detected, as it would alter the state of
the quantum particles.
Protocols of QKD:
BB84: The first and one of the most famous QKD protocols,
developed by Bennett and Brassard in 1984. Uses polarized photons
to transmit the key.
E91: Proposed by Artur Ekert in 1991, based on quantum
entanglement.
SARG04: A more recent protocol developed by Scarani, Acin,
Ribordy, and Gisin in 2004.
How QKD Works
Quantum Entanglement: Utilizes the properties of quantum
entanglement where a pair of entangled quantum particles are
shared between two parties.
Photon Polarization: Alternatively, uses the quantum state of
photons to establish a random, secret key. Any attempt at
eavesdropping disturbs these states and is detectable.
Key Sifting: Parties compare a subset of their measurements to
detect presence of an eavesdropper.
Applications of QKD
Secure Banking and Financial Transactions
Confidential Government Communications
Military Communications
Advantages and Challenges
Advantages: Provides theoretical security based on the laws of
quantum physics, which is unachievable by classical encryption
methods.
Challenges: Requires highly sophisticated technology and is
currently limited by distance and practical implementation issues.
Advantages of QKD Over Classical Protocols:
Unconditional Security: Provides security based on the fundamental
laws of physics, which do not rely on computational hardness
assumptions.
Future-Proof: As quantum computing advances, QKD remains secure
against such technological leaps, unlike classical protocols.
Detectable Eavesdropping: The quantum nature of the key distribution
allows any interception attempt to be detected immediately.
How Does Protocol BB84 invented in 1984 by Charles Bennett and Gilles Brassard Work?
1.Alice's random bit: Alice generates a random bit (0 or 1) that
will form part of the secret key.
2.Alice's random sending basis: Alice chooses a random basis (+ or
x) to encode her bit. The + basis is for rectilinear polarization
(vertical or horizontal), and the x basis is for diagonal
polarization (45 degrees or 135 degrees).
3.Photon polarization Alice sends: Alice sends a photon polarized
according to the bit and basis she chose. For example, if the bit
is 0 and the basis is +, the photon is vertically polarized (↑).
4.Bob's random measuring basis: Bob randomly chooses a basis (+ or
x) to measure the incoming photon's polarization.
5.Photon polarization Bob measures: Bob measures the photon's
polarization. If his chosen basis matches Alice's, he will
correctly measure the polarization and thus the bit Alice sent.
6.PUBLIC DISCUSSION OF BASIS: Alice and Bob publicly share which
bases they used for each photon. They do not disclose the bit
values.
7.Shared secret key: They discard any bits where their bases did
not match and keep the bits where their bases matched. These
remaining bits form the shared secret key.
How to solve the reliability problem of BB84 protocol?
Device-independent quantum key distribution (DIQKD):
The quantum devices used must be perfectly calibrated, trustworthy, and working exactly as they are expected to.
Twin fields quantum key distribution
Twin fields quantum key distribution (TFQKD) was introduced in 2018, and is a version of DIQKD designed to overcome the fundamental rate-distance limit of traditional quantum key distribution
Quantum Networking
Quantum networking aims to connect quantum computers and other
quantum devices to enable secure communication, distributed
quantum computing, and the realization of a global quantum
internet.
Quantum Internet: A quantum internet would allow for the secure
transmission of quantum information over long distances,
enabling applications such as quantum key distribution, quantum
teleportation, and distributed quantum computing.
Quantum Routers: Quantum routers are devices that can route
quantum information between different nodes in a quantum
network, similar to classical routers in a classical network.
Quantum Repeaters: Quantum repeaters are devices that extend the
range of quantum communication by distributing entanglement over
multiple segments, overcoming the limitations of quantum
decoherence and signal loss.
Goals
Secure Communication: Quantum key distribution (QKD) protocols
leverage the principles of quantum mechanics to generate
encryption keys that are theoretically immune to eavesdropping
or interception.
Efficient Information Processing:Shor's algorithm for integer
factorization and Grover's algorithm for unsorted database
search, promise exponential speedups over classical
counterparts in certain computational tasks.
Quantum Networking: Quantum networks could enable secure
communication, distributed quantum computing, and the
realization of a global quantum internet..
IBM Quantum System Two
Current Challenges in Quantum Communication
Distance Limitations: The range of quantum communication is currently
limited. Quantum signals degrade over distance due to loss in optical
fibers or free space.
Quantum Decoherence: Quantum information is susceptible to
environmental interference, leading to rapid loss of coherence, which
disrupts communication.
High Costs and Complexity: Current quantum technologies are expensive
and complex to implement and maintain, limiting widespread adoption.
Quantum decoherence
The decomposition of quantum signals over distance, often referred to as signal loss or decoherence
Thermal Noise: Heat in the environment can cause quantum states to
fluctuate unpredictably.
Vibrational Interactions: In optical fibers, vibrations or
fluctuations can alter the path and state of photons.
Electromagnetic Interference: External electromagnetic fields can
change the energy levels of quantum particles, affecting their quantum
states.
Future Solutions and Research Directions
Quantum Repeaters: These devices are designed to extend the range of
quantum communication by segmenting the transmission distance into
shorter intervals, each supported by quantum entanglement distributed
across these segments.
Error Correction Techniques: Quantum error correction schemes are
being developed to detect and correct errors that arise from
decoherence and other quantum noise without needing to measure the
quantum state directly.
Advanced Materials and Technologies: Research into better materials
for optical fibers and more efficient photon detectors is ongoing,
aiming to reduce loss and improve signal fidelity.