Quantum faqs
Curious about the quantum world? Check out our FAQs to learn more.
Quantum physics, quantum mechanics and quantum technology, what are them?
The field of quantum physics arose in the late 1800s and early 1900s and is the study of matter and energy at the most fundamental level. It aims to uncover the properties and behaviours of the very building blocks of nature and may reveal how everything in the universe (or in multiple universes) is connected to everything else through higher dimensions that our senses cannot comprehend.
Quantum mechanics is a branch of physics dealing with the behaviour of matter and light on the atomic and subatomic scales. It attempts to account for the properties of molecules and atoms and their constituent. These properties include the interactions of the particles with one another and with electromagnetic radiation (i.e., light, X-rays, and gamma rays).
Quantum technologies rely on the properties of quantum mechanics, especially quantum entanglement, quantum superposition, and quantum tunneling. Quantum computing, sensors, cryptography, simulation, measurement, and imaging are all examples of emerging quantum technologies.
Classical and quantum computers present many differences in their computing capabilities and operational features. A quantum computer uses a quantum property called superposition, or qubits, to store data. Unlike a classical computer whose bits of data can exist as either a zero or a 1, a qubit can be a zero, 1, or both simultaneously. This capacity of qubit greatly enhances the computational power of the quantum computer, resulting in the ability to solve several real-world problems way faster than classical computers.
From a hardware perspective, quantum computers typically resemble a chandelier with an intricate system of wires and tubes, a design which is intended to isolate the qubits from electrical, magnetic, and thermal noise from the outside.
Cryptography is considered a field that will be completely disrupted by the advent of quantum computers in the near future.
Classical and quantum computers, what is the difference between them and what risks does the latter pose to cryptography?
Quantum computers will be available in the near future, should we already protect current cryptographic systems against this threat?
Present-day public-key cryptography is believed to offer security against an eavesdropper equipped with a powerful conventional computer. Quantum computers exploit the laws of quantum mechanics to perform calculations, in principle, substantially faster than classical computers, allowing the so-called ‘quantum advantage’. Remarkably, some of the hard problems that have been demonstrated to empower the quantum advantage are at the basis of the current and wide-used protocols for key distribution, meaning that the security of today’s cryptography will potentially be broken by the upcoming quantum machines.
Furthermore, well before more powerful conventional and quantum computers become available, current cryptographic techniques based on computational complexity already present an inherent generic vulnerability to the phenomenon “store now, decrypt later” i.e., when encrypted data is intercepted during transmission and stored in its encrypted form to be then decrypted once more powerful (quantum) computers are available.
Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC) are two fields of quantum cryptography.
QKD is a quantum protocol for generating symmetric cryptographic keys for ultra-secure communications, which enables two or more communicating users to produce and share a symmetric random secret key known only to them, which they can use to encrypt and decrypt their messages. A unique property of QKD is the ability of the communicating users to always detect the presence of a third party attempting to obtain key information.
PQC refers to cryptographic algorithms (usually public-key algorithms) that are thought to be secure against a cryptanalytic attack by a quantum computer. The security of these algorithms relies on the assumption that a given mathematical problem is hard to solve for any computational device, including future quantum computers. PQC is thus usually computationally secure but not information-theoretically secure.
As widely different use cases exist where quantum-resistant cryptography technology is needed, it is foreseen that both technologies will co-exist.
Quantum Key Distribution and Post-Quantum Cryptography, what is the difference between the two approaches in protecting communications against quantum threats?
Information-theoretically secure, what does it mean?
Quantum Key Distribution (QKD) is information-theoretically secure (or unconditionally secure). This means that the security of the system is based on information-theoretic principles, so that it is immune even to attackers with unlimited computational power and resources.
QKD is a physical layer method that allows future-proof data encryption, exhibiting a secure way of distributing random keys between distant users. The basic elements of a QKD system are a transmitter (Alice unit) and a receiver (Bob unit), each of which is referred to as a QKD module. A QKD link connects the QKD modules, potentially with the help of a quantum relay point. The keys are shared via the QKD link which usually consists of a quantum channel and a classical channel. The quantum channel is reserved for quantum signals, such as a single-photon-level coherent state of light, to transmit random bit strings. The classical channel is reserved for synchronization and data exchange (information reconciliation procedure) between the QKD modules.
How does a Quantum Key Distribution system work?
Discrete Variable (DV) and Continuous Variable (CV) QKD, what is the difference?
Most Quantum Key Distribution (QKD) protocols can be classified as either a discrete-variable (DV) protocol or a continuous-variable (CV) one, based on how classical information is being encoded.
In Discrete Variable QKD (DV-QKD) the quantum signals prepared and sent by the emitter (Alice unit) to the receiver (Bob unit) are very weak single photons with encoded random data. This data is then encoded by using a discrete-valued parameter of the photons, for instance their polarization. By using single-photon detectors, the Bob unit measures the state of the arriving photons and distils the secret key.
In Continuous-Variable QKD (CV-QKD), the quantum signals are typically light with information encoded in the quadrature of its electromagnetic fields. CV-QKD uses coherent homodyne or heterodyne detection to continuously retrieve the quadrature value of the light to distil the key.
In conclusion, DV-QKD or CV-QKD can be seen as complementary technologies with different application spaces.
Current QKD systems on the market are fully integrable in existing telecom networks, with apparatuses able to operate both in the C-band and in the O-band configuration (i.e., the systems can work both in dark-fibre mode and also in co-existence with classical communication data multiplexed into the same fibre). Furthermore, they can be used in any network configuration: point-to-point links, trusted nodes configuration and more advanced network topologies (i.e., ring or star networks).
Are Quantum Key Distribution systems integrable with existing telecom networks?
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