Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Advanced Quantum Communication Protocols

Paul G. Kwiat

Published Dec 17, 2005• 0 citations
OpenAlex

Abstract

We have realized the first demonstration of "relativistic" quantum cryptography, using both faint laser pulses and entangled photons. By incorporating an optical delay cavity, Bob is able to measure every photon from Alice in the correct basis, leading to enhanced key rates, as well as some security advantages. We have also implemented our proposal for a high-speed quantum random number generator, in which the arrival time of a detected photon is used to generate -8 random bits per photon. Our system produced cryptographically secure bits at over 4 Mbits/s, with a clear path toward even higher rates. In addition, we solved a number of technical problems to produce 99%-fidelity polarization-entangled pairs from a diode-laser pumped source. Extending our previous implementation of remote state preparation, we have incorporated hyperentanglement to successfully remotely prepare entangled states. Finally, we studied the use of hyperentangled photons as a resource for improved quantum dense coding. Although our experimental verification is still in progress, we identified the theoretically optimal configuration, and compared hyperentangled and multi-pair encoding.

Related papers

Hyperentanglement for advanced quantum communication

Julio T. Barreiro, Paul G. Kwiat

Quantum entanglement is known to enable otherwise impossible feats in various communication protocols, such as quantum key distribution and super-dense coding. Here we describe efforts to further enhance the usual benefits, by incorporating quantum states that are simultaneously entangled in multiple degrees of freedom – “hyperentangled”. Via the process of spontaneous parametric down conversion, we have demonstrated photon pairs simultaneously entangled in polarization and spatial mode, and have used these to realize remote entangled state preparation, full polarization Bell-state analysis, and the highest reported capacity quantum dense coding.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Sep 5, 2008•5 citations

Using hyperentanglement for advanced quantum communication

Trent Graham

"The field of quantum information science promises incredible enhancements in computing, metrology, simulation, and communication, but the challenge of creating, manipulating, and measuring the large quantum states has limited current implementations of such techniques. Such limitations affect photonic quantum information in particular, because photons lack the strong nonlinear interactions required for building up many-particle entangled states and performing multi-photon gates; nevertheless, because photons are currently the only ""flying qubit"", i.e., qubits that are mobile, they are a required resource for quantum communication protocols. One strategy to partially mitigate this limitation is to encode multiple entangled qubits on the different degrees of freedom of a single pair of photons. Such ""hyperentangled"" quantum states may be created with enough qubits to enable a whole new class of quantum information experiments. Furthermore, while nonlinear interactions are required to implement multi-qubit gates between qubits encoded on different particles, such gates can be implemented between qubits encoded on the same particle using only linear elements, enabling a much broader class of measurements. We use hyperentangled states to implement various quantum communication and quantum metrology protocols. Specifically, we demonstrate that hyperentangled photons can be used to increase the classical channel capacity of a quantum channel, transport quantum information between two remote parties efficiently and deterministically, and efficiently characterize quantum channels. We will discuss how to produce, manipulate, and measure hyperentangled states and discuss how entanglement in multiple degrees of freedom enables each technique. Finally, we discuss the limitations of each of these techniques and how they might be improved as technology advances."

•Apr 14, 2016•3 citations

Entanglement in quantum communication : preparation and characterization of photonic qubits

Daniel Ljunggren

At the heart of quantum physics lies the principle of superposition, and at the heart of information theory lies the bit. Perhaps the most useful property of quantum systems is that they can be loaded with information bits, so-called qubits, that are indefinitely both 0 and 1 until a measurement is made. Another consequence is that several qubits can become entangled, which is manifested by the non-classical correlations between such quantum systems when measured in all possible bases. Within the rapidly progressing fields of quantum information and quantum communication these quantum effects are utilized to perform tasks such as quantum computing and quantum cryptography. In this thesis we present experimental and theoretical work using single photon sources to prepare ``flying'' photonic qubits. We describe work using mainly quasi-phase-matched nonlinear crystals to generate beams of entangled photon pairs, that are either encoded in polarization at near-visible wavelengths, or in time at optical fiber telecommunication wavelengths (1550 nm). The optical fiber is the medium used for transporting the qubits over a long distance, and it is therefore essential to couple the photons well into the fibers. By focusing the beams optimally, we have investigated how this problem can meet the requirement of creating photons of a narrow frequency bandwidth and a high photon flux. Furthermore, we have generated truly single photons that are heralded by an electrical signal. As a result of modifying the statistics of such sources we have been able to show the effect of photon antibunching. In two separate works, we have implemented a quantum key distribution system based on faint laser pulses at the telecom wavelength of 1550 nm, as well as protocols based on entanglement for performing authentication of key distribution in quantum cryptography.

•Jan 1, 2006•0 citations

Enhanced on-chip quantum random number generation using combined path and time-delay encoding

P. Pewkhom, N. Palakachen, Poompong Chaiwongkhot +2 more

We present an integrated photonic quantum random number generator combining photon-path selection and time-delay encoding methods to efficiently produce high-quality random bits. True random number generators, particularly quantum-based random number generators, play a critical role in secure communications, cryptographic protocols, and simulations, as they provide genuine unpredictability derived from fundamental quantum processes. This study presents the development of an optical random number generator utilizing a photonic chip, resulting in a very stable, compact, and high key-to-signal ratio device. Our setup employs an attenuated pulsed laser source combined with a photonic circuit featuring a multi-mode interference, whose outputs are monitored by single-photon avalanche diodes. For photon-path encoding, a von Neumann extractor effectively reduces output bias by discarding correlated detection events. In addition, we measure photon arrival times (time-delay encoding) using a novel bin-merging and modulo-based encoding strategy to counteract hardware-induced biases, achieving near-ideal bit uniformity. Experimental results show that combining both encoding techniques doubles the bit-generation rate compared to path-encoding only, achieving 0.49 bits per signal while simultaneously meeting stringent randomness criteria validated by passing all tests in the NIST statistical test suite.

AIP Advances•Jul 1, 2025•1 citation

Relativistic Quantum Cryptography

Evan R. Jeffrey, Joseph B. Altepeter, Paul G. Kwiat

Using entangled photons and a low-loss optical delay, we implement a novel quantum cryptography protocol in which every photon contributes to the key, yielding enhanced efficiency, and an advantage for six- versus four-basis state protocols.

Frontiers in Optics•Jan 1, 2006•4 citations

Advanced Quantum Communication Systems

Evan R. Jeffrey

In addition to implementing these protocols, we have improved several resources for quantum communication and quantum computing. Specifically, we have developed improved sources of polarization-entangled photons, a low-loss quantum memory for polarization qubits, and a quantum random number generator. These tools may be applied to a wide variety of future quantum and classical information systems.

•Jan 1, 2007•4 citations
We have realized the first demonstration of "relativistic" quantum cryptography, using both faint laser pulses and entangled photons. By incorporating an optical delay cavity, Bob is able to measure every photon from Alice in the correct basis, leading to enhanced key rates, as well as some security advantages. We have also implemented our proposal for a high-speed quantum random number generator, in which the arrival time of a detected photon is used to generate -8 random bits per photon. Our system produced cryptographically secure bits at over 4 Mbits/s, with a clear path toward even higher rates. In addition, we solved a number of technical problems to produce 99%-fidelity polarization-entangled pairs from a diode-laser pumped source. Extending our previous implementation of remote state preparation, we have incorporated hyperentanglement to successfully remotely prepare entangled states. Finally, we studied the use of hyperentangled photons as a resource for improved quantum dense coding. Although our experimental verification is still in progress, we identified the theoretically optimal configuration, and compared hyperentangled and multi-pair encoding.
Quantum entanglement is known to enable otherwise impossible feats in various communication protocols, such as quantum key distribution and super-dense coding. Here we describe efforts to further enhance the usual benefits, by incorporating quantum states that are simultaneously entangled in multiple degrees of freedom – “hyperentangled”. Via the process of spontaneous parametric down conversion, we have demonstrated photon pairs simultaneously entangled in polarization and spatial mode, and have used these to realize remote entangled state preparation, full polarization Bell-state analysis, and the highest reported capacity quantum dense coding.
"The field of quantum information science promises incredible enhancements in computing, metrology, simulation, and communication, but the challenge of creating, manipulating, and measuring the large quantum states has limited current implementations of such techniques. Such limitations affect photonic quantum information in particular, because photons lack the strong nonlinear interactions required for building up many-particle entangled states and performing multi-photon gates; nevertheless, because photons are currently the only ""flying qubit"", i.e., qubits that are mobile, they are a required resource for quantum communication protocols. One strategy to partially mitigate this limitation is to encode multiple entangled qubits on the different degrees of freedom of a single pair of photons. Such ""hyperentangled"" quantum states may be created with enough qubits to enable a whole new class of quantum information experiments. Furthermore, while nonlinear interactions are required to implement multi-qubit gates between qubits encoded on different particles, such gates can be implemented between qubits encoded on the same particle using only linear elements, enabling a much broader class of measurements. We use hyperentangled states to implement various quantum communication and quantum metrology protocols. Specifically, we demonstrate that hyperentangled photons can be used to increase the classical channel capacity of a quantum channel, transport quantum information between two remote parties efficiently and deterministically, and efficiently characterize quantum channels. We will discuss how to produce, manipulate, and measure hyperentangled states and discuss how entanglement in multiple degrees of freedom enables each technique. Finally, we discuss the limitations of each of these techniques and how they might be improved as technology advances."
At the heart of quantum physics lies the principle of superposition, and at the heart of information theory lies the bit. Perhaps the most useful property of quantum systems is that they can be loaded with information bits, so-called qubits, that are indefinitely both 0 and 1 until a measurement is made. Another consequence is that several qubits can become entangled, which is manifested by the non-classical correlations between such quantum systems when measured in all possible bases. Within the rapidly progressing fields of quantum information and quantum communication these quantum effects are utilized to perform tasks such as quantum computing and quantum cryptography. In this thesis we present experimental and theoretical work using single photon sources to prepare ``flying'' photonic qubits. We describe work using mainly quasi-phase-matched nonlinear crystals to generate beams of entangled photon pairs, that are either encoded in polarization at near-visible wavelengths, or in time at optical fiber telecommunication wavelengths (1550 nm). The optical fiber is the medium used for transporting the qubits over a long distance, and it is therefore essential to couple the photons well into the fibers. By focusing the beams optimally, we have investigated how this problem can meet the requirement of creating photons of a narrow frequency bandwidth and a high photon flux. Furthermore, we have generated truly single photons that are heralded by an electrical signal. As a result of modifying the statistics of such sources we have been able to show the effect of photon antibunching. In two separate works, we have implemented a quantum key distribution system based on faint laser pulses at the telecom wavelength of 1550 nm, as well as protocols based on entanglement for performing authentication of key distribution in quantum cryptography.
We present an integrated photonic quantum random number generator combining photon-path selection and time-delay encoding methods to efficiently produce high-quality random bits. True random number generators, particularly quantum-based random number generators, play a critical role in secure communications, cryptographic protocols, and simulations, as they provide genuine unpredictability derived from fundamental quantum processes. This study presents the development of an optical random number generator utilizing a photonic chip, resulting in a very stable, compact, and high key-to-signal ratio device. Our setup employs an attenuated pulsed laser source combined with a photonic circuit featuring a multi-mode interference, whose outputs are monitored by single-photon avalanche diodes. For photon-path encoding, a von Neumann extractor effectively reduces output bias by discarding correlated detection events. In addition, we measure photon arrival times (time-delay encoding) using a novel bin-merging and modulo-based encoding strategy to counteract hardware-induced biases, achieving near-ideal bit uniformity. Experimental results show that combining both encoding techniques doubles the bit-generation rate compared to path-encoding only, achieving 0.49 bits per signal while simultaneously meeting stringent randomness criteria validated by passing all tests in the NIST statistical test suite.