Several firms, including ID Quantique, MagiQ, and SmartQuantum, are working on turning the esoteric quantum properties of light into money. These firms are trying to sell a way of distributing a cryptographic key that is theoretically theft-proof because it relies on the quirky quantum physics of photons. Such a quantum key distribution system could allow entities with secrets to encode and decode their data for transmission over optical fiber. Quantum key distribution lets two computers generate a key between them by taking advantage of a quantum property of photon. A quantum key can be generated by transmitting a series of bits encoded using one or a few photons per bit and two types of polarization filters
Several firms, including ID Quantique, MagiQ, and SmartQuantum, are working on turning the esoteric quantum properties of light into money. These firms are trying to sell a way of distributing a cryptographic key that is theoretically theft-proof because it relies on the quirky quantum physics of photons. Such a quantum key distribution system could allow entities with secrets to encode and decode their data for transmission over optical fiber. Quantum key distribution lets two computers generate a key between them by taking advantage of a quantum property of photon. A quantum key can be generated by transmitting a series of bits encoded using one or a few photons per bit and two types of polarization filters
Quantum cryptographic key distribution (QKD) systems1 transmit cryptographic key data encoded in the quantum states of individual optical photons with security of the data guaranteed by the fundamental quantum properties of light, rather than by computational complexity or barriers to interception. Beamsplitter attacks are avoided by using single photons, while attempts to read and replace the photons with copies are thwarted by randomly switching between two non-orthogonal bases for the photon states. This so-called 4-state protocol1 forces an eavesdropper trying to read-and-replace photons to induce errors at a minimum rate of about 25%, which can be readily detected by the parties exchanging the key data. Several groups have performed QKD experiments that demonstrate its feasibility2.
The secure distribution of the secret random bit sequences known as {open_quotes}key{close_quotes} material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over {open_quotes}open{close_quotes} multi-km node-to-node optical fiber communications links is possible. We have also constructed a quantum key distribution system for free-space, line-of-sight transmission using single-photon polarization states, which is currently undergoing laboratory testing. 7 figs.
Quantum cryptography renders a cryptographic solution which is imperishable as it fortifies prime secrecy that is applied to quantum public key distribution. It is a prominent technology wherein two entities can communicate securely with the sights of quantum physics. In classical cryptography, bits are used to encode information where as quantum cryptography i.e. quantum computer uses photons or quantum particles and photon's polarization which is their quantized properties to encode the information. This is represented in qubits which is the unit for quantum cryptography. The transmissions are secure as it is depended on the inalienable quantum mechanics laws. The emphasis of this paper is to mark the rise of quantum cryptography, its elements, quantum key distribution protocols and quantum networks.
In so-called private-key cryptographic systems, secure transmission of confi dential information through unprotected channels relies on the exchange of secret keys, known only to the sender, Alice, and the receiver, Bob.Quantum cryptography is based on the properties of quantum mechanics to obtain a provably secure key distribution.Most existing implement ations rely on either the polarization or the phase of very weak pulses of light sent through optical fibers.Recent results by research groups in British Telecom, Los Alamos National Laboratory and at the University of Geneva, have shown that quantum key distribution is possible over distances of tens of kilometers, using only standard telecom cables.However, due to birefringence and the effects of the environment, the polarization at the output of a fiber fluctuates randomly.Therefore, all existing systems need active polarization control.Systems based on phase also require interferometric detection, which necessitates active stabilization of the interferometers.To eliminate these problems, our team, led by Prof. N. Gisin in the Group of Applied Physics at the University of Geneva, is currently developing a new interferometric system implementing phase-encoded quantum key distribution (US patent pending).A schematic of the setup is given in Fig. 1.Its main features are:1) The system is based on time multiplexing, the interfering pulses following exactly the same spatial path, albeit with a small time delay.The interferometer is thus automatically aligned, and needs neither adjustments nor stabilization of the path lengths.2) Use of Faraday mirrors enables all birefringence effects in the fibers to be cancelled out.Therefore, the system does not require any polarization control.With this new system, Alice and Bob could exchange their cryptographic keys through standard telecom systems.They would be provided with a sending kit and
Due to the fast-paced advancements of the quantum computing field, current public key cryptographic protocols need to be rethought. One promising solution is Quantum Key Distribution (QKD), whose security is robust to any computational advancement. The security of QKD relies on the laws of quantum mechanics, ensuring that any eavesdropper attempting to access the data will be detected. In particular, polarization-encoding QKD systems allow to generate secret keys in two remote locations to encode/decode information, using the State of Polarization (SOP) of single photons. Although its security has been theoretically proven, its practical implementation poses some challenges, part of which are the main focus of this PhD thesis. One relevant process in QKD systems is the synchronization between the transmitter and receiver, namely, the frame synchronization. This way, in this thesis, a frame synchronization method is developed and implemented, showing its potential for the use in prepare-and-measure QKD systems. The developed method has been shown to be effective, even with a low number of photons reaching the receiver. Furthermore, its architecture allows it to be adjusted for different attenuation regimes of the QKD system. The ability to encode data on the physical properties of single photons, in this case, polarization, highly depends on the capacity to accurately generate the required polarization states on demand. This way, an automatic SOP generation method, comprising an optical polarization monitoring system and a dedicated algorithm was developed and implemented, capable of generating four SOPs. This method reached an average Quantum Bit Error Rate (QBER) of 0.75%, which is well below the security threshold. After the SOP generation, and their transmission through the quantum channel, polarization alignment algorithms are required to compensate for the random rotations induced by birefringence in the optical fiber. In this thesis, a non-iterative polarization compensation method was implemented. This method requires only three QBER estimations to re-align the polarization, reaching average QBERs of 1.8%. Additionally, multiple iterative methods were implemented for comparison purposes, with the results clearly showing a better efficiency of the deterministic method. Beyond fiber-based transmissions, free-space transmissions were analysed due to their ability to reach sites without installed fiber and due to its potential for satellite-based quantum communications. This thesis demonstrates the feasibility of polarization-encoding QKD over free-space channels, by subjecting quantum signals to atmospheric turbulence to study its impact. In that sense, polarization variations over a 1.8 km outdoor free-space channel were monitored, to understand the effect of atmospheric turbulence on polarization. These results have shown that SOP variations in free-space links are slow, allowing their compensation. Furthermore, it was identified that, under conditions tested, the Secret Key Rate (SKR) could reach values up to 8.7×10ˉ⁴ bits per second, allowing QKD over free space for distances up to 2.31 km.