Beam Splitter Definition & Meaning

A beam splitter, as used in quantum key distribution (QKD), is a mechanism that divides photons and polarizes them. Beam splitters can divide beams of light linearly or diagonally. In quantum cryptography, this polarization process allows the photons (known as bits in cryptography) to appear in two different states to the interacting parties. The two parties (Alice and Bob) will see bits as 0 or 1.

The following example of a coin flipping protocol one of the methods of performing quantum key distribution between two parties illustrates how a beam splitter works in QKD. To begin the coin flipping protocol, a method used between two mistrustful parties, Alice uses a beam splitter to polarize photons, per quantum physics principles. The beam splitter divides the photons. The generated quantum bits, or qubits, she then sends to Bob. Bob also uses a beam splitter to polarize the photons and records the resulting bit measurements, often measured as either 0 or 1 like traditional bits. He sends those to Alice to compare results. If Alice has the same results, she will then confirm that. Alice and Bob will then use the bits that had the same polarization to create a secret encryption key. The process is largely invisible to users and handled by encryption software.

Beam splitters can also be used by an attacker to interrupt or eavesdrop on the key creation process. The attacker (Eve) can use a beam splitter to intercept photons as Alice sends them to Bob, which will not cause a disturbance in quantum mechanics as most eavesdropping in quantum cryptography does. Eve may then be able to control what she sends to Bob, interfering with their secret quantum key distribution process. Alice and Bob no longer have a secure channel in which they can create a secret key. Security issues such as beam splitting attacks and other interferences like light injection must be addressed in quantum encryption systems.






Jenna Phipps
Jenna Phipps
Jenna Phipps is a contributor for websites such as Webopedia.com and Enterprise Storage Forum. She writes about information technology security, networking, and data storage. Jenna lives in Nashville, TN.

Top Articles

Huge List Of Texting and Online Chat Abbreviations

From A3 to ZZZ we list 1,559 text message and online chat abbreviations to help you translate and understand today's texting lingo. Includes Top...

How To Create A Desktop Shortcut To A Website

This Webopedia guide will show you how to create a desktop shortcut to a website using Firefox, Chrome or Internet Explorer (IE). Creating a desktop...

The History Of Windows Operating Systems

Microsoft Windows is a family of operating systems. We look at the history of Microsoft's Windows operating systems (Windows OS) from 1985 to present...

Hotmail [Outlook] Email Accounts

  By Vangie Beal Hotmail is one of the first public webmail services that can be accessed from any web browser. Prior to Hotmail and its...

Unregulated Power Supply Definition...

An unregulated power supply is a system that transforms input voltage into direct...

Cybersecurity Awareness Training Definition...

Cybersecurity awareness training informs employees of the attack surfaces and vectors in their...

OST File Definition &...

An OST file, or offline storage table (.ost) file, is an Offline Outlook...