Teleportation Channel Research Articles

Non-maximally Entangled Mixed States of X and Non-X Types as Teleportation Channels

Non-maximally Entangled Mixed States of X and Non-X Types as Teleportation Channels

Deterministic All-Optical Quantum Teleportation of Four Degrees of Freedom.

Quantum teleportation, disembodied transfer of the unknown quantum state between two locations, has been experimentally demonstrated for both discrete and continuous variable states in one degree of freedom (DOF). Generally, multiple DOFs are needed to fully characterize a quantum state. Therefore, to implement intact quantum teleportation, multiple DOFs of quantum state should be teleported simultaneously. Recently, teleporting a single photon encoded in two DOFs has been experimentally demonstrated in discrete variable regime. However, the teleportation of more than two DOFs remains unexplored. Here, by utilizing continuous variable hyperentanglement in four DOFs (azimuthal and radial indexes of Laguerre-Gaussian mode, frequency, and polarization), we experimentally demonstrate deterministic all-optical quantum teleportation of four DOFs. Moreover, we experimentally construct 24 parallel teleportation channels. Our results pave the way for deterministically implementing multiple-DOF quantum communication protocols.

Toy gravizap for black hole redemption

In this note we discuss a topological realization of the quantum teleportation protocol. Such a realization facilitates keeping track of the evolution of quantum correlations in the system. It is then suggested, that an implementation of a similar protocol can serve as a toy model of a process of information transfer between causally disconnected regions, such as the one that should take place in a unitary evolution of a quantum black hole. Hawking quanta provide the necessary entangled pairs for the teleportation channel, and the same interaction mechanism that creates the Hawking pairs, destroys the entanglement at the late stages of the evolution. Different steps of the teleportation protocol are characterized by the entropies associated with the disconnected regions, and one can introduce an analog of the Page curve for the entropy of the Hawking radiation. Some regions of the “black hole” interior appear to actually encode the information of the exterior, so it is natural to identify them with the “islands” of the semiclassical gravity analysis.

Port-based entanglement teleportation via noisy resource states

Port-based teleportation (PBT) represents a variation of the standard quantum teleportation and is currently being employed and explored within the field of quantum information processing owing to its various applications. In this study, we focus on PBT protocol when the resource state is disrupted by local Pauli noises. Here, we fully characterise the channel of the noisy PBT protocol using Krauss representation. Especially, by exploiting the application of PBT for entanglement distribution necessary in realizing quantum networks, we investigate entanglement transmission through this protocol for each qubit considering noisy resource states, denoted as port-based entanglement teleportation (PBET). Finally, we derive upper and lower bounds for the teleported entanglement as a function of the initial entanglement and the noises. Our study demonstrates that quantum entanglement can be efficiently distributed by protocols utilizing large-sized resource states in the presence of noise and is expected to serve as a reliable guide for developing optimized PBET protocols. To obtain these results, we address that the order of entanglement of two qubit states is preserved through the local Pauli channel, and identify the boundaries of entanglement loss through this teleportation channel.

Concatenated deleting machines and their characteristics

In this work, we study the performance of one shot and concatenated deleting machines (DMs). We show that the output state of one shot DMs are mixed inseparable, and do not violate Bell’s inequality but can be used as a teleportation channel for all values of the input state parameters. On the other hand, we observe in the concatenation of different DMs that the output states are mixed inseparable and do not violate Bell’s inequality, and cannot be used as a teleportation channel. Further, some important attributes such as inseparability, violation of Bell’s inequality, and teleportation fidelity of the DMs remain unchanged under the order of concatenation. In this context of a teleportation channel, one shot DMs are useful when compared to concatenated DMs.

Robustness of a teleported state influenced by dipole interaction and magnetic field under intrinsic decoherence

A pair of entangled states is teleported through a class of a two-qubit XYZ-Heisenberg chain model in the presence of dipole–dipole interaction and magnetic field. The exact solution of the teleportation channel is obtained via using the intrinsic decoherence master equation. The dynamics of the teleported entanglement, quantum steering, and degree of non-locality are studied. It is found that the setting parameter of the input state plays a central role in the robustness of quantum correlations, where these correlations increase as the input state exists maximally entangled state. The increase in strength of the channel’s parameters restrains the three kinds of quantum correlations, where the small values of dipole–dipole, magnetic field, and decoherence parameters improve the quantum correlation of teleported state. The hierarchy of the three quantum correlations is satisfied for small values of channel parameters, while entanglement, steering, and non-locality are significantly identical at large values of these parameters.

Teleportation of the entangled state of two superconducting qubits

An efficient scheme is proposed to teleport an entangled state of two superconducting (SC) qubits from Alice's to Bob's lab. This type of two-level systems has recently attracted a lot of attention due to the possible tunability of the coupling strength of the qubits with each other. To achieve the purpose, we first generate the GHZ state as the necessary teleportation channel. Then, appropriate interactions are performed in two processes between two of the five qubits, each with a certain frequency modulative external magnetic field which is applied on specific one of the qubits. Next, via applying proper gates and measurements in each lab, we observe that the teleportation can be successfully performed with maximum possible values of fidelity and success probability. At last, to make the protocol close to reality, decay rates of SC qubits are also taken into account, showing that our protocol still works well, satisfactorily.

Enhancing quantum teleportation fidelity under decoherence via weak measurement with flips

Noiseless quantum channels are critical to share a pure maximally entangled state for performing an ideal teleportation protocol. However, in reality the shared entanglement severely degraded due to decoherence. In this paper, we propose a quantum teleportation channel protection scheme to enhance the teleportation fidelity in presence of decoherence. Before the entangled pair enters the decoherence channel, the weak measurement and flip operations are applied to transfer the qubit to a more robust state to the effects of the noise. After the decoherence channel the reversed flip operations and weak measurement reversal are applied to recover the initial state. We illustrate our protected teleportation scheme and compare it with a protocol based on weak measurement reversal. The numerical results show that the average teleportation fidelity of our proposed scheme can be significantly improved. Although the proposed entanglement protection scheme is probabilistic, after a successful entanglement transmission, we use the standard teleportation protocol which has probability one.

Protected Quantum Teleportation Through Noisy Channel by Weak Measurement and Environment-Assisted Measurement

Quantum teleportation as a key protocol for quantum communication and quantum computing demonstrates the stark difference between quantum and classical information transmission. An ideal teleportation protocol requires pure maximally entangled state as the teleportation channel, while in real implementations the shared entanglement is severely degraded due to decoherence. In this letter, we propose a scheme to protect the quantum teleportation from decoherence by means of environment assisted measurement with weak measurements and flip operations. We show that the teleportation fidelity of our proposed scheme is significantly improved compared to teleportation with no protection and a teleportation protocol based on quantum measurement reversal. Also, the explicit formula of average teleportation fidelity and success probability of the entanglement protection are derived.

Characterizing qubit channels in the context of quantum teleportation

We consider a scenario where a party, say, Alice prepares a pure two-qubit (either maximally entangled or non-maximally entangled) state and sends one half of this state to another distant party, say, Bob through a qubit (either unital or non-unital) channel. Finally, the shared state is used as a teleportation channel. In this scenario, we focus on characterizing the set of qubit channels with respect to the final state's efficacy as a resource of quantum teleportation (QT) in terms of maximal average fidelity and fidelity deviation (fluctuation in fidelity values over the input states). Importantly, we point out the existence of a subset of qubit channels for which the final state becomes useful for universal QT (having maximal average fidelity strictly greater than the classical bound and having zero fidelity deviation) when the initially prepared state is either useful for universal QT (i.e., for a maximally entangled state) or not useful for universal QT (i.e., for a subset of non-maximally entangled pure states). Interestingly, in the latter case, we show that non-unital channels (dissipative interactions) are more effective than unital channels (non-dissipative interactions) in producing useful states for universal QT from non-maximally entangled pure states.

Enhanced Uplink Quantum Communication With Satellites via Downlink Channels

In developing the global Quantum Internet, quantum communication with low-Earth-orbit satellites will play a pivotal role. Such communication will need to be two way: effective not only in the satellite-to-ground (downlink) channel but also in the ground-to-satellite channel (uplink). Given that losses on this latter channel are significantly larger relative to the former, techniques that can exploit the superior downlink to enhance quantum communication in the uplink should be explored. In this work we do just that - exploring how continuous variable entanglement in the form of two-mode squeezed vacuum (TMSV) states can be used to significantly enhance the fidelity of ground-to-satellite quantum-state transfer relative to direct uplink-transfer. More specifically, through detailed phase-screen simulations of beam evolution through turbulent atmospheres in both the downlink and uplink channels, we demonstrate how a TMSV teleportation channel created by the satellite can be used to dramatically improve the fidelity of uplink coherent-state transfer relative to direct transfer. We then show how this, in turn, leads to the uplink-transmission of a higher alphabet of coherent states. Additionally, we show how non-Gaussian operations acting on the received component of the TMSV state at the ground station can lead to even further enhancement. Since TMSV states can be readily produced in situ on a satellite platform and form a reliable teleportation channel for most quantum states, our work suggests future satellites forming part of the emerging Quantum Internet should be designed with uplink-communication via TMSV teleportation in mind.

Superposition of causal order enables quantum advantage in teleportation under very noisy channels

We show that the fidelity offered by the standard teleportation protocol under noisy channels applied successively can be significantly improved, when used in conjunction with a quantum switch. In particular, we find that for two such teleportation channels conjugated with an indefinite causal order, teleportation fidelity beyond the classical threshold is achieved for significantly larger noise than would be possible conventionally. One can even make the effective teleportation channel perfectly faithful for very large noise. We also discuss the generalization of our scheme for more than two pathways, and define a figure of merit in that context.

Nonlocality of Majorana zero modes and teleportation: Self-consistent treatment based on the Bogoliubov–de Gennes equation

The nonlocal nature of the Majorana zero modes implies an inherent teleportation channel and unique transport signatures for Majorana identification. In this work we make an effort to eliminate some inconsistencies between the Bogoliubov-de Gennes equation based treatment and the method using the associated regular fermion number states of vacancy and occupation within the `second quantization' framework. We first consider a rather simple `quantum dot--Majorana wire--quantum dot' system, then a more experimentally relevant setup by replacing the quantum dots with transport leads. For the latter setup, based on the dynamical evolution of electron-hole excitations, we develop a single-particle-wavefunction approach to quantum transport, which renders both the conventional quantum scattering theory and the steady-state nonequilibrium Green's function formalism as its stationary limit. Further, we revisit the issue of Majorana tunneling spectroscopy and consider in particular the two-lead coupling setup. We present comprehensive discussions with detailed comparisons, and predict a zero-bias-limit conductance of $e^2/h$ (for symmetric coupling to the leads),which is a half of the popular result of the zero-bias-peak, or, the so-called Majorana quantized conductance ($2e^2/h$). The present work may arouse a need to reexamine some existing studies and the proposed treatment is expected to be involved in analyzing future experiments in this fast developing field.

Featuring Causal Order in Teleportation With Two Quantum Teleportation Channels

Causal order can improve the quantum information transmission in teleportation due a noisy entangled resource being present in it by using additionally an appropriate measurement state on the control state ruling the causal order. In this work, we get analytically the fidelity for the entire process under an arbitrary initialization of such control state and performing an optimal measurement on it, thus obtaining a perfect teleportation. We also analyse other values characterizing the imperfect entangled state where a perfect teleportation can not be reached. Notably, we determine that the best fidelity does not depend on the preparation of the control state but instead on the imperfect initial entangled resource.

Efficient teleportation-based quantum secure communication using quantum channel compression

The paper proposes an efficient protocol for direct secure quantum communication that establishes cryptographic keys between two parties. It relies on two-particle teleportation and quantum channel compression (QCC). The teleportation is accomplished via GHZ-like state quantum channel. The process of quantum channel compression is used to encode four-bit symbols into both two-qubit states (Bell states) and two-bit auxiliary symbols. This leads to reducing the overall classical and quantum resources employed to transfer four-bit symbols at any teleportation procedure in the protocol. The novel teleportation-based protocol achieves an efficiency of 0.4 (40%). It is shown that this is the highest value obtained so far by a protocol of this kind.

Teleportation-based quantum secure communication using quantum channel compression

The paper proposes a scheme for quantum secure communication of key strings, which is based on maximally entangled pairs (EPR pairs), teleportation, and quantum channel compression (QCC). Having ensured the security of their quantum channel by means of a standard eavesdropping check communication (called here “QCC eavesdropping check communication”), Alice and Bob begin the message translation phase. The latter consists of three steps: (i) encoding (QCC encoding) data into single-qubit systems according to the message (key sequence) intended to be transferred from Alice to Bob, (ii) teleporting the encoded single-qubit systems over the established secure quantum channel, and (iii) extracting (QCC decoding) data from the received via teleportation single-qubit systems. The novel teleportation-based quantum secure communication is characterized with efficiency higher than the efficiency of any other scheme of the same type.

Demonstration of Controlled Quantum Teleportation for Discrete Variables on Linear Optical Devices.

We report an experimental implementation of tripartite controlled quantum teleportation on quantum optical devices. The protocol is performed through bi- and tripartite entangled channels of discrete variables and qubits encoded in the polarization of individual photons. The experimental results demonstrate successful controlled quantum teleportation with a fidelity around 83%, well above the classical limit. By realizing the controlled quantum teleportation through a biseparable state, we show that tripartite entanglement is not a necessary resource for controlled quantum teleportation, and the controller's capability to allow or prohibit the teleportation cannot be considered to be a manifestation of tripartite entanglement. These results open new possibilities for further application of controlled quantum teleportation by lowering the teleportation channel's requirements.

Limitations of teleporting a qubit via a two-mode squeezed state

Recently, a teleportation scheme using a two-mode squeezed state to teleport a photonic qubit, so called a “hybrid” approach, has been suggested and experimentally demonstrated as a candidate to overcome the limitations of all-optical quantum information processing. We find, however, that there exists the upper bound of fidelity when teleporting a photonic qubit via a two-mode squeezed channel under a lossy environment. The increase of photon loss decreases this bound, and teleportation better than this limit is impossible even when the squeezing degree of the teleportation channel becomes infinity. Our result indicates that the hybrid scheme can be valid for fault-tolerant quantum computing only when the photon loss rate can be suppressed under a certain limit.

Entanglement 25 Years after Quantum Teleportation: Testing Joint Measurements in Quantum Networks.

Twenty-five years after the invention of quantum teleportation, the concept of entanglement gained enormous popularity. This is especially nice to those who remember that entanglement was not even taught at universities until the 1990s. Today, entanglement is often presented as a resource, the resource of quantum information science and technology. However, entanglement is exploited twice in quantum teleportation. Firstly, entanglement is the “quantum teleportation channel”, i.e., entanglement between distant systems. Second, entanglement appears in the eigenvectors of the joint measurement that Alice, the sender, has to perform jointly on the quantum state to be teleported and her half of the “quantum teleportation channel”, i.e., entanglement enabling entirely new kinds of quantum measurements. I emphasize how poorly this second kind of entanglement is understood. In particular, I use quantum networks in which each party connected to several nodes performs a joint measurement to illustrate that the quantumness of such joint measurements remains elusive, escaping today’s available tools to detect and quantify it.

Experimental Study of Nonclassical Teleportation Beyond Average Fidelity.

Quantum teleportation establishes a correspondence between an entangled state shared by two separate parties that can communicate classically and the presence of a quantum channel connecting the two parties. The standard benchmark for quantum teleportation, based on the average fidelity between the input and output states, indicates that some entangled states do not lead to channels which can be certified to be quantum. It was recently shown that if one considers a finer-grained witness, then all entangled states can be certified to produce a nonclassical teleportation channel. Here we experimentally demonstrate a complete characterization of a new family of such witnesses, of the type proposed in Phys. Rev. Lett. 119, 110501 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.110501 under different conditions of noise. We report nonclassical teleportation using quantum states that cannot achieve average fidelity of teleportation above the classical limit. We further use the violation of these witnesses to estimate the negativity of the shared state. Our results have fundamental implications in quantum information protocols and may also lead to new applications and quality certification of quantum technologies.