Quantum Information Communication Research Articles

Topological Qubits as Carriers of Quantum Information in Optics

Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear optical systems, the most common realm for quantum communication. In particular, it is shown that winding number qubits appear in several aspects of such systems, including quantum electromagnetic states of spin, momentum, orbital angular momentum, polarization of beams of particles propagating in free-space, optical fiber, beam splitters, and optical multiports.

Transmitting qubits through relativistic fields

Wireless communication derives its power from the simultaneous emission of signals in multiple directions. However, in the context of quantum communication, this phenomenon must be reconciled carefully with the no-cloning principle. In this context, we here study how wireless communication of quantum information can be realized via relativistic fields. To this end, we extend existing frameworks to allow for a non-perturbative description of, e.g. quantum state transfer. We consider, in particular, the case of 1+1 spacetime dimensions, which already allows for a number of interesting scenarios, pointing to, for example, new methods for tasks similar to quantum secret sharing.

Teleportation through the wormhole

ER=EPR allows us to think of quantum teleportation as communication of quantum information through space-time wormholes connecting entangled systems. The conditions for teleportation render the wormhole traversable so that a quantum system entering one end of the ERB will, after a suitable time, appear at the other end. Teleportation requires the transfer of classical information outside the horizon, but the classical bit-string carries no information about the teleported system; the teleported system passes through the ERB leaving no trace outside the horizon. In general the teleported system will retain a memory of what it encountered in the wormhole. This phenomenon could be observable in a laboratory equipped with quantum computers.

Encryption and Information Network

Universal grammar assumes the existence of an innate structure common to all human languages. As with secret keys shared by two parties in cryptography, the innateness of language may be related to the continuity of language that both parties share. In other words, discrete language alone cannot construct continuous semantics, which therefore implies the innateness of continuity as proposed in universal grammar. This is also seen in the unique capacity to communicate quantum information, which contains continuity, using discrete language. On the other hand, ever since the development of quantum theory, its probabilistic nature during the measurement process has been debated, particularly by using the phenomenon of entanglement and nonlocality. Since a number of practical applications of quantum theory have been introduced more recently, various techniques of manipulating entanglement have been examined. In particular, it has been noted that for a given chain of non-maximal correlations, there exists a class of coefficients such that entanglement swapping yields the optimal result, namely the weakest link in the chain. A numerical comparison between the general coefficients and the optimal non-maximal states in the case of four and five 2-level entanglement is also provided.

Entangled Photon Source of Quantum Key Generator from Micro Ring Resonator for QKD Use

The powerful novel invention of entangled photon source by using a nonlinear silica micro ring resonator for quantum cryptography use was established and investigated. This entangled photon pair was generated under the degenerated four wave mixing process under the phase mismatch adjusment. The corresponding entangled photon generation Hamiltonian was established and studied in term of EPR pair. The obtained entangled photon pairs can be applied to the quantum cryptography distribution under quantum teleportation process showing the feasible and suitable for quantum information communication via the high visibility and $Q$ factor results. The advantage of this novel entangled photon source will be proved to become a part of quantum distribution device in the near future.

New quantum codes derived from a family of antiprimitive BCH codes

The Bose–Chaudhuri–Hocquenghem (BCH) codes have been studied for more than 57 years and have found wide application in classical communication system and quantum information theory. In this paper, we study the construction of quantum codes from a family of [Formula: see text]-ary BCH codes with length [Formula: see text] (also called antiprimitive BCH codes in the literature), where [Formula: see text] is a power of 2 and [Formula: see text]. By a detailed analysis of some useful properties about [Formula: see text]-ary cyclotomic cosets modulo [Formula: see text], Hermitian dual-containing conditions for a family of non-narrow-sense antiprimitive BCH codes are presented, which are similar to those of [Formula: see text]-ary primitive BCH codes. Consequently, via Hermitian Construction, a family of new quantum codes can be derived from these dual-containing BCH codes. Some of these new antiprimitive quantum BCH codes are comparable with those derived from primitive BCH codes.

Measurement-based formulation of quantum heat engines

There exist two formulations for quantum heat engines that model energy transfer between two microscopic systems. One is the semiclassical scenario and the other is the full quantum scenario. The former is formulated as unitary evolution for the internal system and is adopted by the statistical mechanics community. In the latter, the whole process is formulated as unitary and is adopted by the quantum information community. This paper proposes a model for quantum heat engines that transfer energy from a collection of microscopic systems to a macroscopic system like a fuel cell. In such a situation, the amount of extracted work is visible for a human. For this purpose, we formulate a quantum heat engine as the measurement process whose measurement outcome is the amount of extracted work. Under this model, we derive a suitable energy-conservation law and propose a more concrete submodel. Then we derive a trade-off relation between the measurability of the amount of work extraction and the coherence of the internal system, which limits the applicability of the semiclassical scenario to a heat engine transferring energy from a collection of microscopic systems to a macroscopic system.

Efficiency enhancement for the orbital angular momentum photon quantum interface via single photon frequency upconversion

As the application of orbital angular momentum (OAM) of photon quantum in quantum communication, the OAM photon quantum interface for the transmission wavelength from the telecom communication quantum information storage in visible regime is required. Here we demonstrate the efficiency enhancement for the OAM photon quantum interface based on the frequency upconversion from telecom wavelength to visible regime by sum-frequency generation. The infrared photons at 1 558 nm carrying different OAM values could be converted to the visible regime at 622.2 nm with the optimal efficiency via adjusting the pump beam waist radius and intensity.

Building logical qubits in a superconducting quantum computing system

The technological world is in the midst of a quantum computing and quantum information revolution. Since Richard Feynman’s famous ‘plenty of room at the bottom’ lecture (Feynman, Engineering and Science23, 22 (1960)), hinting at the notion of novel devices employing quantum mechanics, the quantum information community has taken gigantic strides in understanding the potential applications of a quantum computer and laid the foundational requirements for building one. We believe that the next significant step will be to demonstrate a quantum memory, in which a system of interacting qubits stores an encoded logical qubit state longer than the incorporated parts. Here, we describe the important route towards a logical memory with superconducting qubits, employing a rotated version of the surface code. The current status of technology with regards to interconnected superconducting-qubit networks will be described and near-term areas of focus to improve devices will be identified. Overall, the progress in this exciting field has been astounding, but we are at an important turning point, where it will be critical to incorporate engineering solutions with quantum architectural considerations, laying the foundation towards scalable fault-tolerant quantum computers in the near future.

Microscopic modeling of the effect of phonons on the optical properties of solid-state emitters

Understanding the effect of vibrations in optically active nano systems is crucial for successfully implementing applications in molecular-based electro-optical devices, quantum information communications, single photon sources, and fluorescent markers for biological measurements. Here, we present a first-principles microscopic description of the role of phonons on the isotopic shift presented in the optical emission spectrum associated to the negatively charged silicon-vacancy color center in diamond. We use the spin-boson model and estimate the electron-phonon interactions using a symmetrized molecular description of the electronic states and a force-constant model to describe molecular vibrations. Group theoretical arguments and dynamical symmetry breaking are presented in order to explain the optical properties of the zero-phonon line and the isotopic shift of the phonon sideband.

Topological phases with generalized global symmetries

We present simple lattice realizations of symmetry-protected topological phases with $q$-form global symmetries where charged excitations have $q$ spatial dimensions. Specifically, we construct $d$ space-dimensional models supported on a $(d+1)$-colorable graph by using a family of unitary phase gates, known as multiqubit control-$Z$ gates in quantum information community. In our construction, charged excitations of different dimensionality may coexist and form a short-range entangled state which is protected by symmetry operators of different dimensionality. Nontriviality of proposed models, in a sense of quantum circuit complexity, is confirmed by studying protected boundary modes, gauged models, and corresponding gapped domain walls. We also comment on applications of our construction to quantum error-correcting codes, and discuss corresponding fault-tolerant logical gates.

In-vacuum active electronics for microfabricated ion traps.

The advent of microfabricated ion traps for the quantum information community has allowed research groups to build traps that incorporate an unprecedented number of trapping zones. However, as device complexity has grown, the number of digital-to-analog converter (DAC) channels needed to control these devices has grown as well, with some of the largest trap assemblies now requiring nearly one hundred DAC channels. Providing electrical connections for these channels into a vacuum chamber can be bulky and difficult to scale beyond the current numbers of trap electrodes. This paper reports on the development and testing of an in-vacuum DAC system that uses only 9 vacuum feedthrough connections to control a 78-electrode microfabricated ion trap. The system is characterized by trapping single and multiple (40)Ca(+) ions. The measured axial mode stability, ion heating rates, and transport fidelities for a trapped ion are comparable to systems with external (air-side) commercial DACs.

Symmetric Informationally-Complete Quantum States as Analogues to Orthonormal Bases and Minimum-Uncertainty States

Recently there has been much effort in the quantum information community to prove (or disprove) the existence of symmetric informationally complete (SIC) sets of quantum states in arbitrary finite dimension. This paper strengthens the urgency of this question by showing that if SIC-sets exist: (1) by a natural measure of orthonormality, they are as close to being an orthonormal basis for the space of density operators as possible; and (2) in prime dimensions, the standard construction for complete sets of mutually unbiased bases and Weyl-Heisenberg covariant SIC-sets are intimately related: The latter represent minimum uncertainty states for the former in the sense of Wootters and Sussman. Finally, we contribute to the question of existence by conjecturing a quadratic redundancy in the equations for Weyl-Heisenberg SIC-sets.

An exact expression for photon polarization in Kerr geometry

We analyze the transformation of the polarization of a photon propagating along an arbitrary null geodesic in Kerr geometry. The motivation comes from the problem of an observer trying to communicate quantum information to another observer in Kerr spacetime by transmitting polarized photons. It is essential that the observers understand the relationship between their frames of reference and also know how the photon’s polarization transforms as it travels through Kerr spacetime. Existing methods to calculate the rotation of the photon polarization (Faraday rotation) depend on choices of coordinate systems, are algebraically complex and yield results only in the weak-field limit. We give a compact expression for the parallel propagated frame along the null geodesic using Killing-Yano theory, and thereby solve the problem of parallel transport of the polarization vector in an intrinsic geometricallymotivated fashion. The symmetries of Kerr geometry are utilized to obtain a remarkably compact, closed-form expression for the geometrically induced phase of the photon’s polarization. We show that this phase vanishes on the equatorial plane and the axis of symmetry.

Teleporting photonic qudits using multimode quantum scissors

Teleportation plays an important role in the communication of quantum information between the nodes of a quantum network and is viewed as an essential ingredient for long-distance Quantum Cryptography. We describe a method to teleport the quantum information carried by a photon in a superposition of a number d of light modes (a “qudit”) by the help of d additional photons based on transcription. A qudit encoded into a single excitation of d light modes (in our case Laguerre-Gauss modes which carry orbital angular momentum) is transcribed to d single-rail photonic qubits, which are spatially separated. Each single-rail qubit consists of a superposition of vacuum and a single photon in each one of the modes. After successful teleportation of each of the d single-rail qubits by means of “quantum scissors” they are converted back into a qudit carried by a single photon which completes the teleportation scheme.

Information capacity of a single photon

Quantum states of light are the obvious choice for communicating quantum information. To date, encoding information into the polarisation states of single photons has been widely used as these states form an natural closed two state qubit. However, photons are able to encode much more -- in principle infinite -- information via the continuous spatio-temporal degrees of freedom. Here we consider the information capacity of an optical quantum channel, such as an optical fibre, where a spectrally encoded single photon is the means of communication. We use the Holevo bound to calculate an upper bound on the channel capacity, and relate this to the spectral encoding basis and the spectral properties of the channel. Further, we derive analytic bounds on the capacity of such channels, and in the case of a symmetric two-state encoding calculate the exact capacity of the corresponding channel.

A survey on quantum information technology

After nearly three decades of rapid development, the quantum information technology in the theoretical and technical studies has gained remarkable achievements. This review gives a brief introduction to the development of various hot research branches of quantum information technology, including quantum cryptography, quantum communication, quantum computing, quantum simulation, quantum metrology, and fundamental theory of quantum information. In addition, this review also discusses various physical systems which have been well applied in the quantum information technology, such as atomic, molecular and optical physics, different branches in solid state physics (superconducting Josephson Junction system, semiconductor quantum dots, Nitrogen-vacancy color centers in diamond), trapped ions, and nuclear magnetic resonance system. With the investigation and accumulation of quantum information technology, the ability to control microscopic world has been significantly improved. Quantum cryptography has been close to the practical application and the long-distance quantum communication has overcome the practical obstacles in principle. Quantum simulation is close to the limit of the classical computer. Also, quantum metrology has gained rapid development. This review not only shows the situation of the international development of quantum information technology, but also highlights the achievements of China in recent years. These achievements demonstrate that China is an indispensable force in the worldwide quantum information community.

Linking crystals with a single photon

Linking distant quantum memories with light has been a goal of the quantum information community for many years. A team at the University of Geneva has now demonstrated that memories made from rare-earth-ion-doped crystals can be connected using a single photon.

Monogamy of quantum correlations in three-qubit pure states

The limitation on the shareability of quantum entanglement over several parties, the so-called monogamy of entanglement, is an issue that has received considerable attention from the quantum information community over the last decade. A natural question of interest in this connection is whether monogamy of correlations is true for correlations other than entanglement. This issue is examined here by choosing quantum deficit, proposed by A. K. Rajagopal and R. W. Rendell [Phys. Rev. A 66, 022104 (2002)], an operational measure of correlations. In addition to establishing the polygamous nature of the class of three-qubit symmetric pure states characterized by two distinct Majorana spinors (to which the $W$ states belong), those with three distinct Majorana spinors [to which Greenberger-Horne-Zeilinger (GHZ) states belong] are shown to either obey or violate monogamy relations. While the generalized $W$ states can be monogamous or polygamous, the generalized GHZ states exhibit monogamy with respect to quantum deficit. The issue of using monogamy conditions based on quantum deficit to witness the states belonging to stochastic local operations and classical communication (SLOCC) inequivalent classes is discussed in light of these results.

Probing multipartite entanglement in spin chain via structure factors

Multi-qubit entanglement could act as a useful resource for many quantum information communication and processing tasks like quantum networking processes. Genuine non-trivial multi-qubit entanglement could delineates quantum physics from classical physics. Detection of multipartite entanglement however is a theoretical and experimental challenge. A useful tool for this purpose are entanglement witnesses. Recently, we provide an analytical construction of multi-qubit entanglement witnesses using static structure factors (SSF) and study the robustness of the witnesses with respect to noise. In this article, we consider the effectiveness of the entanglement witness based on SSF for probing spin chain.