How does a quantum network differ from a classical network? - by John Bailey and by Assistant - Quora Question Review

This document contains a review of the answer by John Bailey and by Assistant on the question in Quora: "How does a quantum network differ from a classical network?"
To order to read all the answers select: https://www.quora.com/How-does-a-quantum-network-differ-from-a-classical-network

• The text in italics is copied from the article.
  
• Immediate followed by some comments
  

Contents

• 1. Answer Review by John Bailey
• 2. Answer Review by Assistant

Reflection

• Reflection 1 - Question Review

1. Answer Review by John Bailey

A quantum network is constrained by two nasty facts of quantum life.

The No-cloning theorem states that it is impossible to create an identical copy of an arbitrary unknown quantum state. This no-go theorem of quantum mechanics was articulated by James Park in proving the impossibility of a simple perfect non-disturbing measurement scheme, [...] It has profound implications in quantum computing and related fields.[...] No well-defined state can be attributed to a subsystem of an entangled state.
Holevo's theorem proves that given n qubits, although they can "carry" a larger amount of (classical) information (thanks to quantum superposition), the amount of classical information that can be retrieved, i.e. accessed, can be only up to n classical (non-quantum encoded) bits. This is surprising, for two reasons: (1) quantum computing is so often more powerful than classical computing, that results which show it to be only as good or inferior to conventional techniques are unusual, and (2) because it takes 2^n complex numbers to encode the qubits that represent a mere n bits.
Other quantum characteristics should also be considered:

• Bell's theorem
• Gottesman-Knill theorem
• Margolus-Levitin theorem
• No-broadcast theorem
• No-communication theorem
• No-deleting theorem
• No-hiding theorem
• No-teleportation theorem
• PBR theorem
• Quantum threshold theorem

Within this incredibly complex system of constraints, it appears quantum networks will have two specialized applications:
1. computation Networked quantum computing or distributed quantum computing works by linking multiple quantum processors through a quantum network by sending qubits in-between them. Doing this creates a quantum computing cluster and therefore creates more computing potential. Less powerful computers can be linked in this way to create one more powerful processor. This is analogous to connecting several classical computers to form a computer cluster in classical computing. Like classical computing this system is scale-able by adding more and more quantum computers to the network. Currently quantum processors are only separated by short distances.
2. communication In the realm of quantum communication, one wants to send qubits from one quantum processor to another over long distances. This way local quantum networks can be intra connected into a quantum internet. A quantum internet supports many applications, which derive their power from the fact that by creating quantum entangled qubits, https://en.wikipedia.org/wiki/Quantum_entanglement information can be transmitted between the remote quantum processors.

The use of entangled qubits is overrated. There should exist a clear difference between correlation and entanglement. Correlation is a rather simple concept. Entanglement is physical a very difficult concept.

Most applications of a quantum internet require only very modest quantum processors. For most quantum internet protocols, such as quantum key distribution in quantum cryptography, it is sufficient if these processors are capable of preparing and measuring only a single qubit at a time.

2. Answer Review by Assistant

A quantum network differs from a classical network in several key ways due to the principles of quantum mechanics that govern its operations.

A quantum network works as designed. It is the description and most of all the performance of the network that are important.

Here are some of the fundamental differences between quantum networks and classical networks:

• Quantum Superposition: In a quantum network, quantum bits or qubits can exist in a superposition of states, allowing them to represent both 0 and 1 simultaneously. This is in stark contrast to classical bits in a classical network, which can only have a definite state of 0 or 1.
• Quantum Entanglement: Quantum networks can leverage the phenomenon of quantum entanglement, where the states of two or more qubits become correlated in such a way that the state of one qubit instantaneously influences the state of the others, regardless of the distance between them. This feature can enable secure communication and enhanced computational capabilities that are not possible with classical networks.
• Quantum Teleportation: Quantum teleportation is a process in which the state of a qubit can be transmitted from one location to another using entanglement and classical communication. This allows for the transfer of quantum information without physically transporting the qubit itself, which is not possible in classical networks.
• Quantum Key Distribution (QKD): Quantum networks can implement quantum key distribution protocols like BB84 or E91 to securely distribute cryptographic keys between distant parties. QKD ensures that any attempt to eavesdrop on the communication would disturb the quantum states, providing a higher level of security compared to classical key distribution methods.
• Quantum Algorithms: Quantum networks can take advantage of quantum algorithms, such as Shor's algorithm for factoring large numbers exponentially faster than classical algorithms, or Grover's algorithm for searching unsorted databases with a quadratic speedup. These algorithms can potentially solve certain problems much more efficiently than classical algorithms.

For more information about Shor's algorithm select this link: shor.htm
It gives information about the practical problems you can expected.

Noise and Decoherence: Quantum networks are more susceptible to noise and decoherence compared to classical networks. Quantum states are fragile and can easily be disturbed by external factors, leading to errors in quantum computations and communications. Efforts are ongoing to develop error-correction techniques to mitigate these issues.

All of the above information is nice to know, but it is the actual building of such a network, and to test if its performance is such as expected, that gives the final answer.

Overall, quantum networks have the potential to revolutionize information processing, communication, and cryptography by leveraging the unique properties of quantum mechanics. While still in the early stages of development, quantum networks hold promise for enabling new applications and capabilities that are beyond the reach of classical networks.

Go Back to Quora Question Review
Back to my home page Index