{"id":2228,"date":"2026-04-07T10:14:23","date_gmt":"2026-04-07T08:14:23","guid":{"rendered":"https:\/\/www.milq.info\/?page_id=2228"},"modified":"2026-04-07T12:34:07","modified_gmt":"2026-04-07T10:34:07","slug":"chapter4","status":"publish","type":"page","link":"https:\/\/www.milq.info\/en\/qti\/qcomm\/module2\/chapter4\/","title":{"rendered":"Quantum Communication &#8211; Module 2 Chapter 4"},"content":{"rendered":"<div id=\"bsf_rt_marker\"><\/div><p><\/p>\n<h1>CV-QKD<\/h1>\n<p>The implementation of DV-QKD (discrete-variable quantum key distribution) involves considerable challenges. These include the generation of single photons or entangled photon pairs as well as the discrepancy between the theoretically maximal security and a real-world implementation that is inevitably imperfect. This chapter is therefore devoted to a method of quantum key distribution that does not depend on sending and detecting individual photons: CV-QKD (continuous-variable quantum key distribution).<br \/>\nImplementing CV-QKD is demanding as well, yet it represents an interesting alternative to DV-QKD. CV-QKD exploits the wavelike properties of light instead of relying on the particle nature of individual photons. Information is encoded in continuous parameters of the light wave such as amplitude and phase.<br \/>\nIn the preceding chapters the focus was on the photonic, i.e. particle-like, properties of light; the fact that light also exhibits wavelike properties and can be described as an electromagnetic wave was left unaddressed.<\/p>\n<p><video src=\"\/QTIndu\/QComm\/en-2-4-video-1.mp4\" controls=\"controls\" width=\"1920\" height=\"150\"> Dein Browser unterst\u00fctzt dieses Videoformat nicht. Your browser does not support the video tag. <\/video><\/p>\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-100\" class=\"h5p-iframe\" data-content-id=\"100\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"QTI-EN-QComm-2-4-1\"><\/iframe><\/div>\n<hr \/>\n<p>Before we (in a highly simplified way) turn to CV-QKD, we clarify the term modulation. Modulation is a process used in modern classical communication; for that reason the following section will refer extensively to classical communication and be oriented toward it.<br \/>\nIn today\u2019s classical communication the parameters of an electromagnetic wave are used to transmit information or bit sequences. A carrier signal is altered by the signal to be transmitted; this process is called modulation. The carrier must be altered because the signal to be sent cannot be transmitted directly due to technical constraints.<br \/>\nModulation denotes any deliberate alteration of a carrier signal in order to embed information in it. Regardless of whether the signal is sent via radio, optical fibre or satellite, it is modulation that turns a physical wave into a data stream. In classical communication three different properties are usually varied: amplitude, frequency and phase. Many schemes combine two or even all three levers to optimise bandwidth and energy efficiency.<\/p>\n<p><video src=\"\/QTIndu\/QComm\/en-2-4-video-2.mp4\" controls=\"controls\" width=\"1920\" height=\"150\"> Dein Browser unterst\u00fctzt dieses Videoformat nicht. Your browser does not support the video tag. <\/video><\/p>\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-102\" class=\"h5p-iframe\" data-content-id=\"102\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"QTI-EN-QComm-2-4-2\"><\/iframe><\/div>\n<hr \/>\n<p>Modulation is a process applied in today\u2019s classical telecommunications technology. Modulation also plays an important role in CV-QKD. Another crucial aspect is the intensity of the light. In CV-QKD the modulated light is strongly attenuated and quantum effects are exploited.<\/p>\n<p><video src=\"\/QTIndu\/QComm\/en-2-4-video-3.mp4\" controls=\"controls\" width=\"1920\" height=\"150\"> Dein Browser unterst\u00fctzt dieses Videoformat nicht. Your browser does not support the video tag. <\/video><\/p>\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-104\" class=\"h5p-iframe\" data-content-id=\"104\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"QTI-EN-QComm-2-4-3\"><\/iframe><\/div>\n<hr \/>\n<p>The video provided a highly simplified insight into the setup and execution of a CV-QKD scheme. One explicit protocol is the GG02 protocol, introduced in 2002 by Grosshans and Grangier. Following the phases presented in the video, further post-processing steps occur, such as error correction (sliced reconciliation) and privacy amplification. Both steps are necessary: on the one hand to ensure that Alice and Bob possess bit-identical raw data, and on the other hand to guarantee that the key cannot be\u2014or has not been\u2014broken by a potential eavesdropper, Eve.<br \/>\nQuantum physics offers a powerful tool to enhance and enable the security of QKD protocols. It is truly fascinating and impressive that complementary observables cannot be measured simultaneously with arbitrary precision.<br \/>\nIn CV-QKD Alice uses coherent laser light instead of single photons, marking a paradigm shift. The following aspects can be noted with regard to CV-QKD:<\/p>\n<ul>\n<li>Compatibility with existing telecommunication infrastructure<\/li>\n<\/ul>\n<p>One of the major advantages of CV-QKD is its compatibility with existing telecommunication infrastructure. CV-QKD can be operated with standard telecommunication components such as lasers and receivers that are widely used in optical fibre communication networks. This greatly facilitates the adoption of CV-QKD. Integration into already deployed systems is less expensive than with other protocols that require dedicated single-photon detectors.<\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Higher key rates<\/li>\n<\/ul>\n<p>By exploiting the continuous properties of light waves, CV-QKD can achieve higher key rates\u2014the speed at which secure keys are generated\u2014than DV-QKD. This results in faster and more efficient key distribution, a feature that is crucial for applications demanding high data-encryption speeds.<\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Scalability and adaptation to different applications<\/li>\n<\/ul>\n<p>Because CV-QKD is compatible with standard telecommunication equipment, it is easier to scale and to adapt to a wide range of scenarios, from secure high-speed internet connections to safeguarding data in large financial networks. This flexibility is a significant advantage, especially as businesses and governments strive to protect their communications against cyber-threats. CV-QKD provides robust security and offers a seamless path to integrating quantum security into existing networks. This enhances data protection without the need for completely new infrastructure.<\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Demanding post-processing<\/li>\n<\/ul>\n<p>After exchanging the raw measurement data, Alice and Bob must apply post-processing procedures to generate an identical and information-theoretically secure key. Post-processing after the initial distribution of raw data is required in both CV-QKD and DV-QKD because the initially exchanged keys are not always exactly identical (due to eavesdropping attempts, channel disturbances, noise, etc.). However, post-processing in CV-QKD is more complex and computationally intensive than in DV-QKD.<\/p>\n<p>&nbsp;<\/p>\n<p>The security of QKD arises from its ability to detect any attempt to eavesdrop on the communication, a feature enabled by the exploited quantum properties. In this module we have explored various QKD protocols, analysed them, and examined the characteristics of quantum objects. The next module will provide concrete insight into the implementation of a quantum network and will focus specifically on the required hardware.<\/p>\n<hr \/>\n<h2>Exercises:<\/h2>\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-106\" class=\"h5p-iframe\" data-content-id=\"106\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"QTI-EN-QComm-2-4-4\"><\/iframe><\/div>\n<p style=\"text-align: right;\"><a class=\"button\" href=\"https:\/\/www.milq.info\/en\/qti\/qcomm\/module3\/\">Continue to Module 3<\/a><\/p>\n<p><\/p>","protected":false},"excerpt":{"rendered":"<p>CV-QKD The implementation of DV-QKD (discrete-variable quantum key distribution) involves considerable challenges. These include the generation of single photons or entangled photon pairs as well as the discrepancy between the theoretically maximal security and a real-world implementation that is inevitably imperfect. This chapter is therefore devoted to a method of quantum key distribution that does&hellip; <a href=\"https:\/\/www.milq.info\/en\/qti\/qcomm\/module2\/chapter4\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Quantum Communication &#8211; Module 2 Chapter 4<\/span><\/a><\/p>\n","protected":false},"author":8,"featured_media":0,"parent":2207,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2228","page","type-page","status-publish","hentry","without-featured-image"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Quantum Communication - Module 2 Chapter 4 - milq<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.milq.info\/qti\/qcomm\/module2\/chapter4\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Quantum Communication - Module 2 Chapter 4 - milq\" \/>\n<meta property=\"og:description\" content=\"CV-QKD The implementation of DV-QKD (discrete-variable quantum key distribution) involves considerable challenges. 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