Quantum Dense Coding Research Articles

Multiqubit quantum dense coding

Multipartite quantum-information transmission has been a key task for practice purposes and applications in the past decades. In this paper, we present a novel protocol for the multiqubit super dense coding, by using the Greenberger-Horne-Zeilinger (GHZ) states. Our protocol involves measurements doable in the current technique of labs, and thus is possibly realizable and may be extendable to more complicated cases for many systems. In quantum physics, the way the object is measured will affect the code, and the information wont work like puzzles as the condition in general physics which means that, when the divided message is put together, the complete information will be obtained. It requires more complex work to get useful information, like the cooperation of code accepters. To compare with the way in general physics, it is more safe in quantum physics.

Super dense coding out of thermal equilibrium

We have examined the potentiality of superdense coding for a quantum system placed out of thermal equilibrium. To this aim, the dynamics of two two-level quantum systems are analyzed and explicit expressions for transition rates are evaluated. The dependence of superdense coding capacity on initial states is observed and examined for different ratios of anti-symmetric to symmetric transition rates. The effect of sub-radiant and super-radiant terms is interpreted. The validity of dense coding is also analyzed for different probability amplitudes and it is perceived that maximally entangled states show the highest degree of coding capacity. Moreover, the optimal time of coding capacity is greatest for initially entangled state. This strategy can be relevant to analyze further applications out of thermal equilibrium.

Optimal superdense coding capacity in the non-Markovian regime

Superdense coding (SDC) is a significant technique widely used in quantum information processing. Indeed, it consists of sending two bits of classical information using a single qubit, leading to faster and more efficient quantum communication. In this paper, we propose a model to evaluate the effect of backflow information in a SDC protocol through a non-Markovian dynamics. The model considers a qubit interacting with a structured Markovian environment. In order to generate a non-Markovian dynamic, an auxiliary qubit contacts a Markovian reservoir in such a way that the non-Markovian regime can be induced. By varying the coupling strength between the central qubit and the auxiliary qubit, the two dynamical regimes can be switched interchangeably. An enhancement in non-Markovian effects corresponds to an increase in this coupling strength. Furthermore, we conduct an examination of various parameters, namely temperature weight, and decoherence parameters in order to explore the behaviors of SDC, quantum fisher information (QFI), and local quantum uncertainty using an exact calculation. The obtained results show a significant relationship between non-classical correlations and QFI since they behave similarly, allowing them to detect what is beyond entanglement. In addition, the presence of non-classical correlations enables us to detect the optimal SDC capacity in a non-Markovian regime.

Amplifying the capacity of quantum super dense coding by non-Hermitian operations under phase decoherence source

We study the dynamic behavior of quantum super dense coding between two uncoupled qubits, which are immersed in a common Ohmic environment. We examine the validity of local non-Hermitian operations in the amplification of quantum super dense coding. In particular, using analytical and numerical investigations, we show explicitly that the capacity of quantum super dense coding can be greatly amplified with the assistance of a local non-Hermitian operation, i.e. a parity-time symmetric operation. This sheds new light on the protection of quantum super density.

Improving the capacity of quantum dense coding with both spontaneous emission and dephasing by non-Hermitian operation

Using a non-Hermitian operation approach, we propose a scheme to improve quantum dense coding of a qubit-qubit system interacting with a zero-temperature reservoir with both spontaneous emission and dephasing. By solving the master equation of the two-qubit system, we numerically obtain the final capacity of quantum dense coding. The numerical results show explicitly that the non-Hermitian operation indeed helps to improve the non-Hermitian operation from amplitude-phase decoherence. In particular, non-Hermitian operations can protect quantum dense coding more efficiently in the case of strong decay rates than those with small decay rates.

Classical analogue of quantum superdense coding and communication advantage of a single quantum system

We analyze utility of communication channels in absence of any short of quantum or classical correlation shared between the sender and the receiver. To this aim, we propose a class of two-party communication games, and show that the games cannot be won given a noiseless 1-bit classical channel from the sender to the receiver. Interestingly, the goal can be perfectly achieved if the channel is assisted with classical shared randomness. This resembles an advantage similar to the quantum superdense coding phenomenon where pre-shared entanglement can enhance the communication utility of a perfect quantum communication line. Quite surprisingly, we show that a qubit communication without any assistance of classical shared randomness can achieve the goal, and hence establishes a novel quantum advantage in the simplest communication scenario. In pursuit of a deeper origin of this advantage, we show that an advantageous quantum strategy must invoke quantum interference both at the encoding step by the sender and at the decoding step by the receiver. We also study communication utility of a class of non-classical toy systems described by symmetric polygonal state spaces. We come up with communication tasks that can be achieved neither with 1-bit of classical communication nor by communicating a polygon system, whereas 1-qubit communication yields a perfect strategy, establishing quantum advantage over them. To this end, we show that the quantum advantages are robust against imperfect encodings-decodings, making the protocols implementable with presently available quantum technologies.

High-Speed Quantum Radio-Frequency-Over-Light Communication.

Quantum dense coding (QDC) means to transmit two classical bits by only transferring one quantum bit, which has enabled high-capacity information transmission and strengthened system security. Continuous-variable QDC offers a promising solution to increase communication rates while achieving seamless integration with classical communication systems. Here, we propose and experimentally demonstrate a high-speed quantum radio-frequency-over-light (RFOL) communication scheme based on QDC with an entangled state, and achieve a practical rate of 20Mbps through digital modulation and RFOL communication. This scheme bridges the gap between quantum technology and real-world communication systems, which bring QDC closer to practical applications and offer prospects for further enhancement of metropolitan communication networks.

An identity-verifiable quantum threshold group signature scheme based on three-particle GHZ states

With the advancement of the new generation of information technology in recent years, quantum digital signatures have been widely concerned. Among them, quantum threshold group signatures have become a hot research field due to their advantages such as low cost and strong scalability. Therefore, in this paper, we propose an identity-verifiable quantum threshold group signature scheme based on three-particle GHZ states. The characteristics of the scheme are as follows. The signers can reconstruct the key K for signature’s generation and verification by using the Shamir threshold secret sharing scheme. A quantum signature is generated by performing controlled-not operations, von Neumann measurements, and quantum Fourier transform. When the signature is verified, only classical hash values need to be compared, without comparing quantum states. Identity verification is performed between participants by using hash functions. The efficiency of the scheme is improved by using super-dense coding. Security analysis shows that our scheme is unforgeable and undeniable.

Symbolic model checking quantum circuits in Maude.

This article presents a symbolic approach to model checking quantum circuits using a set of laws from quantum mechanics and basic matrix operations with Dirac notation. We use Maude, a high-level specification/programming language based on rewriting logic, to implement our symbolic approach. As case studies, we use the approach to formally specify several quantum communication protocols in the early work of quantum communication and formally verify their correctness: Superdense Coding, Quantum Teleportation, Quantum Secret Sharing, Entanglement Swapping, Quantum Gate Teleportation, Two Mirror-image Teleportation, and Quantum Network Coding. We demonstrate that our approach/implementation can be a first step toward a general framework to formally specify and verify quantum circuits in Maude. The proposed way to formally specify a quantum circuit makes it possible to describe the quantum circuit in Maude such that the formal specification can be regarded as a series of quantum gate/measurement applications. Once a quantum circuit has been formally specified in the proposed way together with an initial state and a desired property expressed in linear temporal logic (LTL), the proposed model checking technique utilizes a built-in Maude LTL model checker to automatically conduct formal verification that the quantum circuit enjoys the property starting from the initial state.

Enhancing the capacity of quantum dense coding from correlated amplitude damping channel via non-Hermitian operation

Using the non-Hermitian operation approach, we propose a scheme to protect and enhance quantum dense coding from correlated amplitude damping (AD) decoherence. In contrast to the results of memoryless AD channel, we show that the memory effects play a significant role in the suppression of quantum dense coding sudden death. Moreover, we find that the damaged quantum dense coding can be effectively enhanced by using the non-Hermitian operation. Furthermore, the freezing phenomenon of quantum dense coding can be detected by using the optimal non-Hermitian operation.

Transformation of Bell states using linear optics

Bell states form a complete set of four maximally polarization entangled two-qubit quantum state. Being a key ingredient of many quantum applications such as entanglement based quantum key distribution protocols, superdense coding, quantum teleportation, entanglement swapping etc, Bell states have to be prepared and measured. Spontaneous parametric down-conversion (SPDC) is the easiest way of preparing Bell states and a desired Bell state can be prepared from any entangled photon pair through single-qubit logic gates. In this paper, we present the generation of complete set of Bell states, only by applying unitary transformations of half-wave plate (HWP) on the initial Bell state. The initial Bell state is prepared using a combination of a nonlinear crystal and a beam-splitter (BS) and the rest of the Bell states are created by applying single-qubit logic gates on the entangled photon pairs using HWPs. Our results can be useful in many quantum applications, especially in superdense coding where control over basis of maximally entangled state is required.

Quantum dense coding and teleportation based on two coupled quantum dot molecules influenced by intrinsic decoherence, tunneling rates, and Coulomb coupling interaction

Quantum dense coding and teleportation based on two coupled quantum dot molecules influenced by intrinsic decoherence, tunneling rates, and Coulomb coupling interaction

Improving the capacity of quantum dense coding via non-Hermitian operation

We propose a novel method to enhance the capacity of quantum dense coding under amplitude damping noise using non-Hermitian operations. With the assistance of non-Hermitian operations, we show that the capacity of quantum dense coding can always be larger than 1 for any two-qubit states. In particular, the non-Hermitian operation can improve quantum dense coding more efficiently in the case of strong decoherence strength than those with small decoherence strength. Our results shed new light on the protection of quantum dense coding in a quantum environment.

High Dimensional Quantum Digital Signature Depending on Entanglement Swapping

While a single qubit information can be carried with a single photon in 2−dimensional quantum technology, it is possible to carry more than one qubit information with a single photon in high-dimensional quantum technologies. The amount of qubit to be transported depends on the size of the system obtained in the high dimension. In other words, the more high-dimensional quantum structure it creates, the more qubit-carrying system is obtained. In this study, a high dimensional quantum digital signature(QDS) scheme is proposed for multi-partied by using entanglement swapping and super-dense coding. QDS, which is proposed as highdimensional, allows more data and high-rate keys to be transferred. Security analysis of propesed QDS in high-dimensional show that the propablity of anyone obtaining information is much lower than in qubit states. Since all data(quantum and classic) in this protocol is instantly sent by using entanglement channels it is more resilient eavesdropping attacks. Today, developments in highdimensional experimental studies show that the high-dimensional QDS proposed in this study can be implemented practically.

Superdense coding for V-shaped channel and cylindrical geometry

We have examined the possibility of quantum dense coding for the V-shaped channel and cylindrical geometry of plasmonic waveguides by assuming certain initial states at different dipole-dipole distances. It is found that the dense coding capacity initially decreases and then gradually increases until it becomes steady (χ = 1) at later time. We also revealed the optimal time valid for super-dense coding regarding each initial state. It is worth noting that dense coding capacity is valid for all other states for a time less than optimal time (t < τ o ) except for pure state. The estimated optimal time for a V-shaped channel is prominent due to greater β-factor accomplishing it as a prosperous geometry for Superdense coding. The greater optimal time for V-shaped channel entitles this geometry a benchmark for the practical applications of quantum information technology.

Mutually Unbiased Measurements, Hadamard Matrices, and Superdense Coding

Mutually unbiased bases (MUBs) are highly symmetric bases on complex Hilbert spaces, and the corresponding rank-1 projective measurements are ubiquitous in quantum information theory. In this work, we study a recently introduced generalisation of MUBs called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mutually unbiased measurements</i> (MUMs). These measurements inherit the essential property of complementarity from MUBs, but the Hilbert space dimension is no longer required to match the number of outcomes. This operational complementarity property renders MUMs highly useful for device-independent quantum information processing. It has been shown that MUMs are strictly more general than MUBs. In this work we provide a complete proof of the characterisation of MUMs that are direct sums of MUBs. We then construct new examples of MUMs that are not direct sums of MUBs. A crucial technical tool for this construction is a correspondence with quaternionic Hadamard matrices, which allows us to map known examples of such matrices to MUMs that are not direct sums of MUBs. Furthermore, we show that–in stark contrast with MUBs–the number of MUMs for a fixed outcome number is unbounded. Next, we focus on the use of MUMs in quantum communication. We demonstrate how any pair of MUMs with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> outcomes defines a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -dimensional superdense coding protocol. Using MUMs that are not direct sums of MUBs, we disprove a recent conjecture due to Nayak and Yuen on the rigidity of superdense coding, for infinitely many dimensions. The superdense coding protocols arising in the refutation reveal how shared entanglement may be used in a manner heretofore unknown.

A fully-connected three-user quantum hyperentangled network

Exploiting the fantastic features of quantum mechanics, a hyperentangled quantum network encoded in multiple degree of freedoms (DOF), e.g., polarization and orbital angular momentum DOFs, can encode more qubits per transmitted photon and offers a promising platform for many dramatic applications. Here, we demonstrate such a hyperentangled multiuser network with a fully connected network architecture by using dense wavelength division multiplexing and entanglement transfer technique. Three hyperentangled states in polarization and time-energy DOFs are multiplexed to three single mode fibers to form the fully connected network architecture. Then, three interferometric quantum gates are utilized for transferring quantum entanglement from time-energy to orbital angular momentum DOF. The experimental results reveal a high quality of the hyperentanglement of the constructed network with the entangled state fidelity of higher than 96%. Our approach can provide a novel way to construct a large-scale hyperentangled network that can support various kinds of quantum tasks like superdense coding and teleportation.

Bipartite entanglement distillation by unilateral and bilateral local filters using polarizing Mach–Zehnder interferometers

The extraordinary correlation seen in entangled states in space-like separated regions is one of the most intriguing aspects of quantum states. Practical utility of entanglement as a resource for quantum key distribution, dense coding, or teleportation generally requires maximally entangled states. In practice, entanglement quality degrades substantially due to channel noise. The problem may be mitigated by entanglement distillation. The simplest distillation protocol is enforced by local filtering operations and classical communication. The local filtering operations are merely generalized positive operator valued measures utilizing additional degrees of freedom (DoFs) as ancillary qubits. In this work, we experimentally show that filtering on a single channel (unilateral) is equally effective as filtering on both channels (bilateral) for distillation of pure non-maximally entangled bipartite states. This result holds for a non-maximally entangled multi-qubit Greenberger-Horne-Zeilinger (GHZ) like states as well, as they show a straightforward extension of the Bell state structure. Further, we provide a theoretical comparison of the efficacy of unilateral and bilateral filtering for the case of mixed states resulting from local depolarizing noise introduced either in one or both of the non-maximally entangled pairs. Surprisingly, when noise is introduced in either one of the channels, we find that unilateral filtering on the noise-free channel outperforms the filtering on the noisy channel and bilateral filtering on both channels. We also find that bilateral filtering is more effective when both channels are noisy. A reduction in the number of local operations, in general, has the advantage of reducing the complexity of the experimental apparatus and the reduction of measurement related errors.

Rigidity of superdense coding

The famous superdense coding protocol of Bennett and Wiesner demonstrates that it is possible to communicate two bits of classical information by sending only one qubit and using a shared EPR pair. Our first result is that an arbitrary protocol for achieving this task (where there are no assumptions on the sender’s encoding operations or the dimension of the shared entangled state) is locally equivalent to the canonical Bennett-Wiesner protocol. In other words, the superdense coding task is rigid . In particular, we show that the sender and receiver only use additional entanglement (beyond the EPR pair) as a source of classical randomness. We also investigate several questions about higher-dimensional superdense coding, where the goal is to communicate one of d 2 possible messages by sending a d -dimensional quantum state, for general dimensions d . Unlike the d = 2 case (i.e. sending a single qubit), there can be inequivalent superdense coding protocols for higher d . We present concrete constructions of inequivalent protocols, based on constructions of inequivalent orthogonal unitary bases for all d &gt; 2. Finally, we analyze the performance of superdense coding protocols where the encoding operators are independently sampled from the Haar measure on the unitary group. Our analysis involves bounding the distinguishability of random maximally entangled states, which may be of independent interest.

Improving the Capacity of Quantum Dense Coding and the Fidelity of Quantum Teleportation by Weak Measurement and Measurement Reversal.

A protective scheme of quantum dense coding and quantum teleportation of the X-type initial state is proposed in amplitude damping noisy channel with memory using weak measurement and measurement reversal. Compared with the noisy channel without memory, the memory factor improves both the capacity of quantum dense coding and the fidelity of the quantum teleportation to a certain extent for the given damping coefficient. Although the memory factor can inhibit decoherence in some degree, it cannot eliminate it completely. In order to further overcome the influence of the damping coefficient, the weak measurement protective scheme is proposed, which found that the capacity and the fidelity can be efficiently improved by adjusting weak measurement parameter. Another practical conclusion is that, among the three initial states, the weak measurement protective scheme has the best protective effect on the Bell-state in terms of the capacity and the fidelity. For the channel with no memory and full memory, the channel capacity of quantum dense coding reaches two and the fidelity of quantum teleportation reaches one for the bit system; the Bell system can recover the initial state completely with a certain probability. It can be seen that the entanglement of the system can be well protected by the weak measurement scheme, which provides a good support for the realization of quantum communication.