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A single photon—An amazing quantum system

Muhammad Suhail Zubairy

Published Sep 14, 2023• 0 citations
Publisher

Abstract

Abstract Maxwell showed that light consists of electric and magnetic fields that oscillate in directions perpendicular to the direction of propagation. Associated with this picture of light as an electromagnetic wave is an important property—the polarization of light. The polarization of light is related to the direction of oscillation of the electric field in an electromagnetic wave. The polarization of a single photon and its counterintuitive behavior is explained. Based on this description of this simplest quantum system, a communication system that can allow perfect security is described. In this so-called BB-84 protocol, a key can be exchanged between two parties on a publicly accessible channel in such a way that an eavesdropper can be traced immediately. This almost magical communication system is based on the foundational ideas of quantum mechanics.

DOI
10.1093/oso/9780198883067.003.0006

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Abstract Maxwell showed that light consists of electric and magnetic fields that oscillate in directions perpendicular to the direction of propagation. Associated with this picture of light as an electromagnetic wave is an important property—the polarization of light. The polarization of light is related to the direction of oscillation of the electric field in an electromagnetic wave. The polarization of a single photon and its counterintuitive behavior is explained. Based on this description of this simplest quantum system, a communication system that can allow perfect security is described. In this so-called BB-84 protocol, a key can be exchanged between two parties on a publicly accessible channel in such a way that an eavesdropper can be traced immediately. This almost magical communication system is based on the foundational ideas of quantum mechanics.
Maxwell showed that light consists of electric and magnetic fields that oscillate in directions perpendicular to the direction of propagation. Associated with this picture of light as an electromagnetic wave is an important property—the polarization of light. The polarization of light is related to the direction of oscillation of the electric field in an electromagnetic wave. In this chapter, the basic principles of quantum mechanics are discussed by studying the polarization property of a single photon. First the properties of a polarizer are presented and Malus’ law for polarized light is derived. Next it is shown that the basic features of quantum mechanics can be understood via an analysis of a single photon passing through a polarizer. This simple system allows an introduction of Dirac’s ket and bra notations for a quantum state. Finally the transformation properties of the quantum beam splitter and the polarization beam splitters are discussed.
We model the Photon as a space lattice oscillation, in a plane perpendicular to its line of propagation. This propagation is at the light velocity c. This plane is vertical or horizontal or rotating clockwise or anticlockwise. This oscillation occupies a finite space volume of a defined shape, structure and size. Papers [1] and [2] model electromagnetism as the geometrodynamics of space; we show that the elastic space lattice oscillating displacement vector is the oscillating electric field, pointing in the opposite direction. For simplicity we ignore the magnetic field. We also show that our photons and ground state photons-the photoms, condense when they are in phase and disperse when in anti-phase. This feature explains the double slit experiment, both for an ensemble of photons (classical EM wave) and single photons. It dispels the need for attributing a dualistic nature to single photons that arrive at the screen one at a time.
Quantum Cryptography is based on the use of subatomic particles (photons) and their intrinsic quantum properties (photon polarization) to develop an unbreakable system. It is not possible to measure the quantum state of any system without affecting the system. This property provides secure transmission of key between sender and receiver. Quantum Cryptography is a way to combine the relative ease and convenience of key exchange in public key cryptography with the ultimate security of a one-time pad. Quantum techniques for key distribution, the classically impossible task of distributing secret information over an insecure channel whose transmissions are subject to inspection by an eavesdropper, between parties who share no secret key initially. Quantum Cryptography uses the principles of Quantum Mechanics to implement a cryptographic system. The key problem which is solved by using quantum techniques is that of eavesdropping detection. The bits are represented as qubits, physically modeled by photons, and communicated over a quantum channel. The polarization states of photons represent 0's and 1's. Keyword: Asymmetric key, Cryptography, Protocols, Quantum, symmetric key
Abstract In this work, we propose a quantum key distribution protocol using the polarization and transverse spatial degrees of freedom of single photons. We show that the protocol is secure and easy to implement experimentally, thus being able to be used in investigations on optical communication. In addition, we show that the information transmitted between two separate parties is always greater than the information retained by a eavesdropper. In this way, it is always possible to employ classical error correction and privacy amplification to minimize eavesdropper information.
Quantum communication is an important branch of quantum technology. It can safely transmit private information between legitimate parties and its unconditional security is guaranteed by quantum physics. So far, deterministic secure quantum communication without entanglement usually transmits single photons in two-way quantum channels. We propose a deterministic secure quantum communication proposal, and it requires a one-way quantum channel and a classical channel. In our protocol, a sender encodes logical bits by using two conjugate bases consisting of the polarization and time-bin degrees of freedom of a photon and transmits it to a receiver over a quantum channel. Upon receiving this photon, the receiver measures it randomly in two bases and can decode the bit deterministically with the help of the sender. Any attack from eavesdroppers will be detected by the legitimate parties. Furthermore, this protocol can be implemented with linear-optic elements and single-photon detectors.
Modern communication in absolute secrecy requires creation of new intrinsically secure quantum communication channels. It is particularly necessary during the first connection between two parties establishing then in assumed unconditional security the secret cryptographic key which is supposed to be used afterwards during normal information exchanging. This new emerging field of quantum information technology is based on a new type of light sources, in which numbers of emitted photons can be carefully controlled. Especially advantageous are sources of single photons emitted at strictly predetermined moments, so called single-photon devices. Then any possible eavesdropper activity will be followed by some unavoidable disturbance which alerts both communication parties to an event. In the present paper, the Purcell effect associated with enhancement of spontaneous emission coupled to a resonator is explained, methods used to produce streams of antibunched photons are given, mechanisms applied to control carrier injection into quantum dots are shown and some possible designs of single-photon devices are presented and described. These devices are based on taking advantage of both the Purcell effect and the atom-like energy spectrum of quantum dots.