There are two prominent families of Quantum Key Distribution (QKD) protocols: 

However, the cost-effectiveness of employing a quantum channel compared to information security alternatives remains to be determined. Examples of such options include key extension, using an additional classical channel for key distribution, or combining multiple classical channels to create a composite key. Additionally, there is uncertainty regarding the prediction that quantum computing will rapidly break RSA codes, which has driven acceleration in this field.

Regardless of cost-effectiveness, the motivation to advance quantum communication is increasing. For example:

• A point-to-point (P2P) experimental network for key distribution was established for several clients in London (Toshiba in collaboration with Ernst & Young, May 2022).
• Two Singapore data centers were connected via a quantum channel (June 2023).
• A QKD-based optical network was set up between Brussels and Mechelen, Belgium (a collaboration between Nokia and Proximus, June 2023).

In the initial phase, the Continuous Variable protocol will likely be implemented in encryption systems (similar to the early phase of hybrid cars). These protocols offer a higher level of security than classical channels and require only endpoint modifications rather than major changes to urban network infrastructure. However, the resilience of these protocols remains a topic of debate.

Quantum theory has existed for over 100 years, and its applications are an integral part of our daily lives, including technologies such as lasers, optical communication, and semiconductors. The fields currently considered notable innovations are:

• Quantum Computing – Based on technologies like superconductors, ions, neutral atoms, and more recently, transistors on silicon substrates.
• High-Sensitivity Sensors – Examples include gravimeters, magnetometers, and atomic clocks based on laser-atom interactions.
• Development of New Quantum Materials.
• Quantum Encryption – Quantum key distribution (QKD), which is part of the cybersecurity market.

Cybersecurity Market

The cybersecurity market is vast, with an estimated value of approximately $223 billion in 2023, according to Research and Markets, and a high growth rate exceeding 10%. This market includes software for network protection, data centers, and databases; electronic devices such as computers and mobile phones; complex electronic systems like vehicles and airplanes; and critical infrastructures. Essentially, it encompasses nearly all electronic systems.

Alongside this market, the past few years have seen massive investments in the quantum field. According to the World Economic Forum, approximately $30 billion was invested in quantum technologies by 2022. Israel ranks 11th globally in quantum investment distribution. These investments are driving various technologies, including quantum computers. Such advancements have raised concerns that developing robust computational capabilities might be used to break encryption systems. In response, the field of quantum communication has rapidly advanced.

According to Markets and Markets, the quantum encryption market was valued at approximately $0.5 billion, with a high growth rate of about 40% projected over the next five years. By 2028, the market is expected to reach approximately $3 billion.

The primary technologies being developed in this field include:

• Quantum Encryption Protocols (e.g., Ekert 92, BB84, Continuous Variable).
• Quantum Random Number Generators (QRNGs).
• Optical Crystals, mainly KTP-based, for generating single-photon sources.
• Single-photon detectors (commonly operating at wavelengths of 1500nm and 1300nm) utilizing silicon and superconducting technologies.

The table highlights several key players developing systems with quantum channels, including ID Quantique, Toshiba, and Xanadu. These companies aim to establish end-to-end communication systems for distributing public keys over quantum channels.

QuantumCTek	NEC Corporation	NEC Corporation	QuintessenceLabs
Post-Quantum	Toshiba	Qasky	MagiQ Technologies
Quantum Xchange	Qubitekk	SK Telecom	SeQureNet
Xanadu	KETS Quantum Security

Currently, RSA (Rivest–Shamir–Adleman) encryption, a public key encryption system, is highly prevalent, enabling the exchange of information between two users even when the key is exposed to eavesdropping. It should be noted that data transmitted over the internet is susceptible to interception, and an eavesdropper might capture the public key (the encryption key transmitted over the network). However, breaking the encryption using only the intercepted key (without the private key that generated it) requires immense computational power, meaning significant computing time.

For example, when transmitting information between A (Alice) and B (Bob), the encryption process occurs as follows – Alice generates two keys as described:

Alice sends Bob only the public key over a classical channel (the key is exposed to eavesdropping).

All data transmitted over the Internet is susceptible to eavesdropping. However, breaking the encryption remains computationally challenging, even if the eavesdropper intercepts the public key.

Below are methods to enhance information security and their relation to quantum channels:

• Increasing the length of the public key, for example, from 256 bits to 512 bits, without requiring infrastructural changes (aside from endpoint modifications).
• Additional communication channels for key distribution make it more difficult for an eavesdropper to intercept by requiring simultaneous interception of multiple channels.
• Using a quantum channel (utilizing weakened signals).

A quantum channel is characterized by signals transmitted at such low power that they approach background noise levels. These weakened signals pose a significant technological challenge for eavesdroppers, requiring highly sophisticated detection systems. If an eavesdropper attempts to intercept the signals, they will leave a “signature” in the communication system, such as increased noise levels (measured by the Bit Error Rate). It is worth noting that standard tools exist for detecting such changes in the system, such as the Optical Time Domain Reflectometer (OTDR), which will not be covered in this review.

Currently, there are two primary families of Quantum Key Distribution (QKD) protocols:

1. DV Protocols (Discrete Variable; typically require infrastructural changes and often involve dark fiber):

• Protocols based on single-photon modulation, where information is transmitted using measurements of polarization states (e.g., BB84).
• Protocols utilizing a discrete and generally small number of photons (typically two or three), where the correct “level” (photon count) carries relevant information, while the remaining signals serve as decoys (Decoy State).

2. CV Protocols (Continuous Variable):
These protocols do not require infrastructural changes and are suitable for metropolitan area (Metro) networks. Information is modulated onto the waveform using spectrally narrow coherent light. Detection is typically performed using the Homodyne detection method, necessitating transmitting the laser source to the receiver. The security level of CV protocols is generally lower compared to DV protocols.

Key points to take into consideration:

• The development of new data encryption technologies, alongside technologies designed for eavesdropping, is part of an “endless war” (Counter-Countermeasures).
• A public key alone is insufficient for decrypting encrypted data intercepted over the network (immense computational power is required, depending on the key’s size, or, in other words, significant processing time).
• There are two prominent families of QKD protocols: CV (typically based on waveform modulation using a narrowband source) and DV (based on single-photon or discrete-photon modulation).
• Establishing a quantum channel for key distribution in either of these technologies enhances data security as follows:

1. CV technology can be integrated into metro networks (up to 40 km) without infrastructural changes. However, the security of the quantum channel against eavesdropping in the CV protocol is unclear, as some information may be “leaked,” the channel could be amplified, and the information might be copied. However, the noise level will increase (according to Cloning Theory), which can be detected through network monitoring.
2. DV technology is based on transmitting information via a single photon, for example, by changing its polarization state or via a discrete number of photons, some of which may be entangled (at the time of modulation), allowing simultaneous transmission of identical information to two locations. The presence of an eavesdropper on a channel transmitting information using DV technology will increase the noise level, and if this occurs in a well-engineered system, it can be measured, and the channel will be rejected for key distribution.
3. DV technology is more expensive than CV technology and requires infrastructural changes, and there is a current preference for implementing CV-based technology.

Several issues still need to be solved. The cost-benefit of maintaining a quantum channel compared to other information security alternatives must be clarified, such as key length extension, using an additional classical channel for key distribution, or combining multiple classical channels to create a key from all channels. Additionally, there is uncertainty about the prediction that quantum computing can quickly break RSA codes.

As of today, it seems that CV protocols will be implemented first in encryption systems. These protocols do not require infrastructural changes in urban networks except at the endpoints.

In Israel, one startup company is focused on developing systems for quantum communication, while others have a broader product portfolio in various fields. It is important to note that each company has its agenda; some seek the “Quantum Ready” stamp, meaning certification or proof that a quantum channel can be integrated into a system they are developing, while others see a real need to advance the technology as part of the transmitter-receiver.

QuantLR

The company in Modiin was established in 2018 and specializes in quantum encryption and communication. It has raised approximately $2.5M from private investors and through the OurCrowd platform. It reported that its first commercial product for key distribution over optical fibers was ready in February 2023.

Elisra

A member of the Elbit Group, Elisra employs about 1,500 people with annual sales of $400 million. The company’s main activities include EW, IR, RF, and control and monitoring systems. Elisra participates in a quantum communication consortium and aims to establish a complete quantum communication system (transmission, synchronization, reception) in a Free Space point-to-point topology for short and medium-range distances, based on single-photon sources (BB84 protocol) and entangled photons (BBM92 protocol).

Opsys

Opsys Technologies was founded in 2016 and is located in Holon. Its primary focus is developing high-speed optical communication systems beyond Ethernet networks in various protocols for long-distance systems (Long Haul). Opsys is part of a quantum communication consortium aiming to establish a multi-channel DWDM system that integrates a quantum channel with Add & Drop capabilities for each channel within the 1500nm range. It is important to note that the quantum channel is spectrally close to the information channels in this system.

NVIDIA (formerly Mellanox)

Founded in 1999, the company is headquartered in Yokneam. In 2019, it was acquired by NVIDIA for $6.9B. The company provides components for end-to-end networks, including optical switches, cables, and adapters. It also provides network management services across various protocols and database storage. The company’s primary activity in the quantum communication consortium is the development of transmitters and receivers suitable for quantum key distribution over optical fibers.

Raicol

Raicol was established in 1995, focusing mainly on growing nonlinear crystals for optics. The company is located in the Afek Industrial Park in Rosh HaAyin and has manufacturing and development laboratories. Its primary activities include developing and selling RTP, KTP, PPKTP, and HGTR crystals. In 2022, the company sold crystals worth approximately $12M, with about 80% exported and the rest for local consumption, reporting a net profit of $0.2M. Raicol operates about 150 crystal-growth furnaces and is experiencing significant growth. This is reflected in increased sales, the expansion of furnace numbers, and the search for new products in the crystal sector, especially for the quantum market. Recently, Raicol announced its acquisition by the Japanese company Oxide Cooperation for $25M. The company maintains connections with companies such as Qubitekk.

ID Quantique (Switzerland)

Founded in 2001, ID Quantique emerged from the Applied Physics Group at the University of Geneva. The company develops end-to-end components and systems for quantum encryption. Its products include single-photon detectors in two technologies—superconducting nanowire and silicon detectors—time synchronization sources, a quantum random number generator, and encryption systems for transceiver key distribution rates ranging from 10kB/sec up to 70 km.

3Ki (Canada)

Founded in 2015, 3Ki emerged from the National Research Institute of Science. The company develops entangled light sources, complete encryption systems with a Quantum Bridge, and signal processing systems.

Qtlabs (Germany)

Founded in 2017, Qtlabs specializes in point-to-point QKD systems (transmitter-receiver) over optical fibers at a wavelength of 1500nm based on entangled sources. They also provide SpaceFree QKD systems within the 500-700nm spectral range.

Quintessence Labs (Australia)

Founded in 2008, Quintessence Labs is known for its QKD systems using the C protocol, including its Optica system.

QNULabs (India)

Founded in 2018, its products include QKD systems for optical fiber networks and a quantum random number generator.

LuxQuanta (Spain)

Founded in 2021, LuxQuanta originated from the Institute of Photonic Sciences. The company focuses on developing transceiver systems for quantum key distribution. Its main product is the NOVA LQ transceiver system based on the CV protocol.

ThinkQuantum (Italy)

Founded in 2021, ThinkQuantum emerged from the University of Padua in Italy. The company offers a DV protocol-based QKD system (single-photon modulation) suitable for distances up to 100 km, recommending that the transmission take place over Dark Fiber (without additional channels).

• June 2023 – Nokia and Proximus announced the successful establishment of a QKD-based optical network between Brussels and Mechelen in Belgium.
• June 2023 — Two data centers in Singapore will be connected with a quantum channel. The experiment started in 2022 and is now in its second phase to test relevant applications.
• May 2023 – Scientists from China reported the establishment of a 1000 km (Long Haul) infrastructure for quantum key distribution.
• March 2023 – Scientists from China set a record for QKD distribution at a rate of 110 Mb/sec over a distance of more than 10 km, ten times faster than the previous record.
• January 2023 – A European program was announced to build a quantum communication infrastructure (QCI) for quantum key distribution as part of the European Union’s cybersecurity efforts.
• May 2022 – Toshiba and Ernst & Young announced the establishment of a point-to-point QKD-based experimental network for several clients in London.

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