This paper presents an in-depth exploration of Quantum Spread Spectrum Code Division Multiple Access (QSSCDMA) communication systems. By manipulating the shape of quantum photon wavepackets and utilizing high-speed electro-optical modulators, we demonstrate the potential for spread spectrum encoding of quantum states of light for CDMA communication systems. This work builds on the classical spread spectrum technology’s strengths—namely, its robust interference management and low probability of intercept—by broadening the spectrum of transmitted signals through quantum mechanical principles. We rigorously characterize the mathematical framework underpinning quantum spread spectrum techniques, offering a comprehensive theoretical analysis and demonstrating the viability of QSS-CDMA systems. Our findings establish a foundation for future research and development in quantum communication systems, paving the way for advanced multi-user quantum networks.
This paper presents an in-depth exploration of Quantum Spread Spectrum Code Division Multiple Access (QSSCDMA) communication systems. By manipulating the shape of quantum photon wavepackets and utilizing high-speed electro-optical modulators, we demonstrate the potential for spread spectrum encoding of quantum states of light for CDMA communication systems. This work builds on the classical spread spectrum technology’s strengths—namely, its robust interference management and low probability of intercept—by broadening the spectrum of transmitted signals through quantum mechanical principles. We rigorously characterize the mathematical framework underpinning quantum spread spectrum techniques, offering a comprehensive theoretical analysis and demonstrating the viability of QSS-CDMA systems. Our findings establish a foundation for future research and development in quantum communication systems, paving the way for advanced multi-user quantum networks.
This paper describes the fundamental principles and mathematical foundations of Quantum Direct-Sequence Spread-Spectrum Code Division Multiple Access (QDSS-CDMA) communication systems. The evolution of quantum signals through the quantum direct-sequence spread-spectrum multiple access communication system is carefully characterized by a novel approach called the decomposition of creation operators. In this methodology, the creation operator of the transmitted quantum signal is decomposed into the chip-time interval creation operators each of which is defined over the duration of a chip. These chip-time interval creation operators are the invariant building blocks of the spread-spectrum quantum communication systems. With the aid of the proposed chip-time decomposition approach, we can find closed-form relations for quantum signals at the receiver of such a quantum communication system. Further, the paper details the principles of narrow-band filtering of quantum signals required at the receiver, a crucial step in designing and analyzing quantum communication systems. We show that by employing coherent states as the transmitted quantum signals, the inter-user interference appears as an additive term in the magnitude of the output coherent (Glauber) state, and the output of the quantum communication system is a pure quantum signal. On the other hand, if the transmitters utilize particle-like quantum signals (Fock states) such as single photon states, entanglement effect can arise at the receivers. The important techniques developed in this paper are expected to have far-reaching implications for various applications in the exciting field of quantum communications and quantum signal processing.
This paper describes the fundamental principles and mathematical foundations of quantum spread spectrum code division multiple access (QCDMA) communication systems. The evolution of quantum signals through the direct-sequence spread spectrum multiple access communication system is carefully characterized by a novel approach called the decomposition of creation operators. In this methodology, the creation operator of the transmitted quantum signal is decomposed into the chip-time interval creation operators each of which is defined over the duration of a chip. These chip-time interval creation operators are the invariant building blocks of the spread spectrum quantum communication systems. With the aid of the proposed chip-time decomposition approach, we can find closed-form relations for quantum signals at the receiver of such a quantum communication system. Further, the paper details the principles of narrow-band filtering of quantum signals required at the receiver, a crucial step in designing and analyzing quantum communication systems. We show that by employing coherent states as the transmitted quantum signals, the inter-user interference appears as an additive term in the magnitude of the output coherent (Glauber) state, and the output of the quantum communication system is a pure quantum signal. On the other hand, if the transmitters utilize particle-like quantum signals (Fock states) such as single photon states, entanglement and a spread spectrum version of the Hong-Ou-Mandel effect can arise at the receivers. The important techniques developed in this paper are expected to have far-reaching implications for various applications in the exciting field of quantum communication and signal processing.
Barcoding photons, atoms, and any quantum states can provide a host of functionalities that could benefit future quantum communication systems and networks beyond today's imagination. As a significant application of barcoding photons, we introduce code division multiple-access (CDMA) communication systems for various applications. In this context, we introduce and discuss the fundamental principles of a novel quantum CDMA (QCDMA) technique based on spectrally encoding and decoding of continuous-mode quantum light pulses. In particular, we present the mathematical models of various QCDMA modules that are fundamental in describing an ideal and typical QCDMA system, such as quantum signal sources, quantum spectral encoding phase operators, M×M quantum broadcasting star-coupler, quantum spectral phase decoding operators, and the quantum receivers. Following the above discussions, we then elaborate on a QCDMA system with M users. In describing a QCDMA system, this paper considers a unified approach where the input continuous-mode quantum light pulses can take on any form of pure states such as quantum coherent (Glauber) states and quantum number (Fock) states. The mathematical presentation is independent of the form of the input pure quantum states. We show that the spectrally encoded quantum states of the light at the quantum star-coupler output are not, in general, factorized states, except for input Glauber states. For input number states, one can observe features like entanglement and quantum interference. Moreover and interestingly, as a consequence of Heisenberg's uncertainty principle, the quantum signals sent by photon number states obtain complete phase uncertainty at the time of measurement. Therefore, at the receiver output, the multiaccess inter-signal interference vanishes. Due to Heisenberg's uncertainty principle, the received signal intensity at the photodetector's output, right at the time of measurement, changes from coherent detection scheme for input Glauber states to incoherent detection scheme for input number states. We also would like to highlight that the mathematical models and tools developed in this paper, in the context of QCDMA, become very useful for developing and analyzing other quantum multiple-access techniques based on wavelength, space and time domain. Furthermore, our mathematical model is valuable in signal design and data modulations of point-to-point quantum communications, quantum pulse shaping, and quantum radar signals and systems where the inputs are continuous mode quantum signals. QCDMA may open up novel possibilities for various quantum technologies such as data privacy, distributed quantum computation, quantum internet, and anti-jamming quantum communication systems.
We show that communication of single-photon quantum states in a multi-user environment is improved by using spread spectrum communication techniques. We describe a framework for spreading, transmitting, despreading, and detecting single-photon spectral states that mimics conventional spread spectrum techniques. We show in the cases of inadvertent detection, unintentional interference, and multi-user management, that quantum spread spectrum communications may minimize receiver errors by managing quantum channel access.
We show that communication of single-photon quantum states in a multi-user environment is improved by using spread spectrum communication techniques. We describe a framework for spreading, transmitting, despreading, and detecting single-photon spectral states that mimics conventional spread spectrum techniques. We show in the cases of inadvertent detection, unintentional interference, and multi-user management, that quantum spread spectrum communications may minimize receiver errors by managing quantum channel access.
Spread-spectrum techniques are widely used in radio communication and telecommunication. Any signal like acoustic, electrical, and electromagnetic signal produced with a specific bandwidth is spread in frequency hence results in a wider bandwidth. Spread spectrum techniques are deployed in telecommunication because of many significant advantages, e.g., to achieve secure communications, to detect the eavesdropping, to resist natural interference, to bound power flux density for satellite down links and resistance to noise and jamming. In spread spectrum technique, frequency hopping (FH) is used as a basic modulation technique by which any telecommunication signal can be transmitted on a wider bandwidth (radio bandwidth) as compared to frequency value of the original signal. Spread spectrum techniques deploy FH, direct sequence (DS), or mix of both methods so that it can be used for multiple access and reduces the interference to other receivers to get the overall privacy. At the receiver side, the received signals are correlated to extract the original information being sent. The two main motivation behind spread spectrum are: to create anti-jamming for unauthenticated person and to provide low probability of interception. The classical data transmission can also be achieved by using quantum communication protocols like dense coding, quantum key distribution (QKD), and quantum teleportation. Most of these protocols use quantum states of light to transmit the information through optical fibers. The problem of channel access become apparent when number of users increases. In classical communication networks, when many users want to use the same channel at the same time, many multiple access methods are used. On the other side, quantum communication networks also deploy frequency and wavelength division multiple access techniques, hence each user make use of same channel at different frequencies and different time instance. In addition to this, many multiple access techniques employ orbital angular momentum of single photons and coherent states. Quantum spread spectrum multiple access scheme described here for optical fibers could be used for free-space data transmission. In this scheme, multiple users send their photons via same optical fiber, sharing their path, time window, and frequency band. A number of techniques have been proposed previously for data transmission for quantum optical communication which provides heavy losses while combining and separating the transmitted data from different users. The described scheme is developed to follow classical spread spectrum methods, and also follows add-drop architecture with simple extraction and combination points.