In the last few years quantum information has played an increasingly central role in the research activities of many scientists within wide ranging areas of physics, mathematics and computer science as it known to be more efficient than its classical counterpart. The impact and advantages of quantum information protocols emerge in numerous situations. In the case of cryptography, quantum dynamics guarantees secure protocols, and in quantum computation, factorization of large numbers, intractable with classical algorithms, can be solved much faster with a quantum computer. It is now widely believed that quantum information will play a leading role in future technologies. Together with the ongoing development of more efficient schemes to solve both new and old tasks in information science, a great deal of interest has been devoted to selecting suitable physical systems where one could realize these ideas. In particular, the quest for large scale integrability has stimulated an increasing interest in the field of solid state physics. Nanoelectronics seems the natural arena to realize physical implementation of quantum hardware. Qubits made out of solid-state devices, such as spins/charges in quantum dots or superconducting nanocircuits, may offer a greater advantage in this respect because fabrication techniques allow for scalability to a large number of coupled qubits. Recent experimental breakthroughs in semiconducting and superconducting nanostructures constitute the first important steps towards the realization of a solid-state quantum computer. In addition the interest in solid state quantum computation has stimulated a large body of research aimed at understanding the properties of entanglement in solid state systems. This Focus issue of New Journal of Physics gathers together contributions from leading experts in the area of solid state quantum information with the aim of providing a panorama of the most exciting scientific questions currently being investigated in the field. Focus on Solid State Quantum Information Contents Quasiparticle entanglement: redfinition of the vacuum and reduced density matrix approach P Samuelsson, E Sukhorukov and M Buttiker Pseudospin quantum computation in semiconductor nanostructures V W Scarola, K Park and S Das Sarma Superconducting qubit network with controllable nearest-neighbour coupling M Wallquist, J Lantz, V S Shumeiko and G Wendin Weak coupling Josephson junction as a current probe: effect of dissipation on escape dynamics J M Kivioja, T E Nieminen, J Claudon, O Buisson, F Hekking and J P Pekola The single Cooper-pair box as a charge qubit K Bladh, T Duty, D Gunnarsson and P Delsing Quantum state transfer in arrays of flux qubits A O Lyakhov and C Bruder Spin filling of a quantum dot derived from excited-state spectroscopy L H Willems van Beveren, R Hanson, I T Vink, F H L Koppens, L P Kouwenhoven and L M K Vandersypen Clauser–Horne inequality for the full counting statistics F Taddei, R Fazio and E Prada Recent advances in exciton based quantum information processing in quantum dot nanostructures H J Krenner, S Stufler, M Sabathil, E C Clark, P Ester, M Bichler, G Abstreiter and J J Finley Spatially highly resolved study of AFM scanning tip-quantum dot local interaction S Kicin, A Pioda, T Ihn, M Sigrist, A Fuhrer, K Ensslin, M Reinwald and W Wegscheider Transfer of entanglement from electrons to photons by optical selection rules M Titov, B Trauzette, B Michealis and C W J Beenakker Non-Abelian Chern-Simons models with discrete gauge groups on a lattice B Doucot and L B Ioffe Landau–Zener transitions in qubits controlled by electromagnetic fields Martijn Wubs, Keiji Saito, Sigmund Kohler, Yosuke Kayanuma and Peter Hänggi Phase-slip flux qubits J E Mooij and C J P M Harmans Mediated tunable coupling of flux qubits Alec Maassen van den Brink, A J Berkley and M Yalowsky Divergent beams of nonlocally entangled electrons emitted from hybrid normal-superconducting structures Elsa Prada and Fernando Sols Decoherence from ensembles of two-level fluctuators Josef Schriefl, Yuriy Makhlin, Alexander Shnirman and Gerd Schön Semiconductor quantum dots for electron spin qubits W G van der Wiel, M Stopa, T Kodera, T Hatano and S Tarucha Rosario Fazio, NEST-INFM and Scuola Normale Superiore, Pisa, Italy
In the last few years quantum information has played an increasingly central role in the research activities of many scientists within wide ranging areas of physics, mathematics and computer science as it known to be more efficient than its classical counterpart. The impact and advantages of quantum information protocols emerge in numerous situations. In the case of cryptography, quantum dynamics guarantees secure protocols, and in quantum computation, factorization of large numbers, intractable with classical algorithms, can be solved much faster with a quantum computer. It is now widely believed that quantum information will play a leading role in future technologies. Together with the ongoing development of more efficient schemes to solve both new and old tasks in information science, a great deal of interest has been devoted to selecting suitable physical systems where one could realize these ideas. In particular, the quest for large scale integrability has stimulated an increasing interest in the field of solid state physics. Nanoelectronics seems the natural arena to realize physical implementation of quantum hardware. Qubits made out of solid-state devices, such as spins/charges in quantum dots or superconducting nanocircuits, may offer a greater advantage in this respect because fabrication techniques allow for scalability to a large number of coupled qubits. Recent experimental breakthroughs in semiconducting and superconducting nanostructures constitute the first important steps towards the realization of a solid-state quantum computer. In addition the interest in solid state quantum computation has stimulated a large body of research aimed at understanding the properties of entanglement in solid state systems. This Focus issue of New Journal of Physics gathers together contributions from leading experts in the area of solid state quantum information with the aim of providing a panorama of the most exciting scientific questions currently being investigated in the field. Focus on Solid State Quantum Information Contents Quasiparticle entanglement: redfinition of the vacuum and reduced density matrix approach P Samuelsson, E Sukhorukov and M Buttiker Pseudospin quantum computation in semiconductor nanostructures V W Scarola, K Park and S Das Sarma Superconducting qubit network with controllable nearest-neighbour coupling M Wallquist, J Lantz, V S Shumeiko and G Wendin Weak coupling Josephson junction as a current probe: effect of dissipation on escape dynamics J M Kivioja, T E Nieminen, J Claudon, O Buisson, F Hekking and J P Pekola The single Cooper-pair box as a charge qubit K Bladh, T Duty, D Gunnarsson and P Delsing Quantum state transfer in arrays of flux qubits A O Lyakhov and C Bruder Spin filling of a quantum dot derived from excited-state spectroscopy L H Willems van Beveren, R Hanson, I T Vink, F H L Koppens, L P Kouwenhoven and L M K Vandersypen Clauser–Horne inequality for the full counting statistics F Taddei, R Fazio and E Prada Recent advances in exciton based quantum information processing in quantum dot nanostructures H J Krenner, S Stufler, M Sabathil, E C Clark, P Ester, M Bichler, G Abstreiter and J J Finley Spatially highly resolved study of AFM scanning tip-quantum dot local interaction S Kicin, A Pioda, T Ihn, M Sigrist, A Fuhrer, K Ensslin, M Reinwald and W Wegscheider Transfer of entanglement from electrons to photons by optical selection rules M Titov, B Trauzette, B Michealis and C W J Beenakker Non-Abelian Chern-Simons models with discrete gauge groups on a lattice B Doucot and L B Ioffe Landau–Zener transitions in qubits controlled by electromagnetic fields Martijn Wubs, Keiji Saito, Sigmund Kohler, Yosuke Kayanuma and Peter Hänggi Phase-slip flux qubits J E Mooij and C J P M Harmans Mediated tunable coupling of flux qubits Alec Maassen van den Brink, A J Berkley and M Yalowsky Divergent beams of nonlocally entangled electrons emitted from hybrid normal-superconducting structures Elsa Prada and Fernando Sols Decoherence from ensembles of two-level fluctuators Josef Schriefl, Yuriy Makhlin, Alexander Shnirman and Gerd Schön Semiconductor quantum dots for electron spin qubits W G van der Wiel, M Stopa, T Kodera, T Hatano and S Tarucha Rosario Fazio, NEST-INFM and Scuola Normale Superiore, Pisa, Italy
Quantum Information Science is a cross-disciplinary subject that has arisen in the last twenty years. It concerns itself with the consequences of our most complete description of the physical world (that is, quantum mechanics) for the reliable, secure, private, and rapid processing of information, both in communication and computation. While its invention is often ascribed to the famous theoretical physicist Richard Feynman in the 1980s, his contributions were only one of many that initiated the field around that time. While he perceived that new types of physical devices, in which the quantum laws of superposition and entanglement function at the logical level, could give new power in the simulation of quantum physics, it was others (Bennett, Brassard) who showed that the uncertainty principle led to fundamentally more secure ways of communicating secret messages. It was yet others (Deutsch, Vazirani) who understood that quantum theory defined a new kind of Turing machine, and that not only quantum physics simulations, but potentially many other computational problems, are sped up in this machine. And it was yet another (Shor) who found a simple, very fast algorithm for prime factorization. The word "qubit" was coined only in 1995. Its introduction is indicative of a new mindset that has developed in recent years for studying and using quantum systems. "Qubit" now stands for a durable paradigm that spans a very wide variety of fields. It thus has many sub-meanings: first, it is the basic abstract unit of information for workers ranging from optical communication engineers to NMR spectroscopists to black-hole theorists. Second, it is the name we now routinely give to physical two level systems, as they are realized by photons, atomic and ionic eigenlevels, electronic and nuclear spin, structural defects in solids, and circulating-current states of superconducting devices. Physics has long dealt with some of these two-level systems, but calling them qubits implies a whole suite of interrelated ideas and capabilities that we ascribe to these systems: the ability to precisely set, and to precisely measure, the quantum state of one unique specimen, to avoid its coupling with the environment while at the same time strongly and controllably coupling the qubits together, to exploit the resulting quantum entanglement as a resource for metrological, cryptographic, and computational tasks. Quantum Information is a very diverse subject pursued today in many different directions, by many hundreds of researchers internationally: In theoretical physics, it has enlivened and sharpened the understanding of efficient representations of entangled many-particle wavefunctions, and has provided the prospect of applications for new concepts such as anyons and majorana fermions. Information theorists has benefitted from having a rigorous extension of the basis of their field, in which classical information theory is subsumed into a greatly broader subject. Theoretical computer scientists continue the search for new quantum algorithms, and have used quantum concepts to prove new results about the classification of computational complexity. Coding theorists have had the new and subtle problem of quantum error correction to analyse and conquer. Most strikingly, the program of experimental physics has been influenced in many directions by Quantum Information Science. State-of-the-art optics experiments transmit quantum states over long distances and perform precision manipulations in single quanta (atomic ions, impurity spins, quantum dots) in the quest to have working quantum cyptography and quantum computing. Quantum Hall systems, and topological insulators, are being assiduously examined for new elementary excitations for use as qubits. In the course of ten years, superconducting devices have improved by over four orders of magnitude in their quantum coherence, a metric made precise by the ideas of quantum computing. [...] DiVincenzo, David
Information is a physical. Physical systems register and process information. These facts generated enormus interest in the development of novel quantum tecnologies, especially because the construction of smaller electronic devices ultimately leads to a consideration of quantum mechanical effects in electronic and computer desingns. The notion of the classical bit of information theory was formally pushed into the realm of the quanta with the introduction of the quantum bit or qubit, in the seminal works of Deutsch (Deutsch, 1985) and Shor (Shor, 1994). They demostrated that, indeed, controlled multipartite qubit interference effects could provide the means for a radical new way of computing, allowing the computation of many intractable computational problems, such as the factoring of large number or exact simulation of large quantum systems. The field of experimental and theoretical research in quantum information and computation has emerged as very important player in the understanding of quantum phenomena the both the basic and technological levels. This has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineerin, to the physical sciences, and we now have an interdisciplinary field where great efforts are being made in order to build devices that allow the progressing of information at a quantum level. A concise introduction to the field of quantum information and quantum computation is presented. This stars with the bassic definitions of bits, quantum registers, through to the universal gate-set for building the universal quantum computer, from a quantum network model of computation. The work shows how two-qubit gates suffice for quantum computation, emphasing the power of the quantum circuit representation for entagling and disentagling quantum states. This leads to the “no-cloning theorem”, which leads us to many interesting applications, such as quantum cryptography. Two alternative approaches or performing quantum computation are also described i) the one-way or measurement based quantum computer method, and ii) holonomic or geometric quantum computation. Following this, quantum entaglement quantification is highlighted, particulary its usefulness as a communication resource, in order to describe some of its most celebrated practical applications to date: quantum teleportation, cryptography, dens coding, and data compression. Deutsch’s concept of quantum parallelism is enphasized in order to gain insight into the potential for efficiently solving certain classically intratable algorithms. A subject central to the field of QIP- quantum decoherence- is then introduced.. Possible ways to overcome it, in particular quantum error correction, are discussed. A descriptios of some of the currently available hardware of the practical implementation of quantum computation is provided with a discussion of the main physical quantum bits that are currently employed (or proposed) for a such a purpose.
The recently emerged field of quantum technology is aiming to employ quantum coherence and entanglement for realization of next generation sensors, standards, imaging systems, secure communication and computers.Although applications of quantum technologies cover a broad spectrum and their development stage varies from early demonstrations to commercially available devices, many challenges have been identified.The first includes tailoring materials for quantum technologies, which is playing an essential role in technological applications of quantum science.Solid state systems allowing long coherence time are essential for quantum computation and quantum sensing.Ultrapure materials with tailored isotopic content are important for reaching long coherence time of spin qubits (Awschalom et al., 2013).The ability to place single dopants with high precision and form spin qubits at desired location is essential for both quantum computing and quantum sensing applications (McCallum et al., 2012;Smith et al., 2019).The performance of different types of qubits is usually benchmarked in terms of controllability and coherence time.Usually solid-state systems allow fast control, but exhibit fast decoherence owing to complex environment.It is therefore important to search for new types of qubits combining isolation from environment and access via fast coherent control and readout.Novel approaches combining different quantum systems into build hybrid quantum devices for optimal performance is a promising avenue.Examples of such hybrid approaches are spin systems coupled to superconducting qubits (Kubo et al., 2011) and hybrid nuclear-electronic qubits (Morley et al., 2013).Optimal protocols for quantum technologies requires extension of coherence time of qubits beyond the coherence time of the isolated quantum system.The efficient protection toolkit includes dynamical decoupling (Yang et al., 2011) and quantum error correction (Terhal, 2015) based techniques.Although general principles of qubits protection were developed and tested experimentally in different model environments, it is essential to adapt them to realistic environmental noise.In the field of quantum sensing, it is also essential to combine protections against noise with non-reduced sensing performance.Experimental imperfections can be addressed using optimal control tools (Glaser et al., 2015).The development of efficient quantum algorithms is another growing field belonging to quantum software area.On one hand, it is essential to find problems where a quantum computer can outperform classical computers.On the other hand, it is essential to develop an application scenario for a limited number of qubits (Montanaro, 2016).In addition, in order to develop new algorithms, future work must include discoveries of application scenarios of already known algorithms.Application of quantum Fourier transform for sensing is a promising example of such new applications (Vorobyov et al., 2021).Signal processing is another field of quantum software that is becoming essential in applications.Advanced signal analysis protocols, like quantum compressed sensing, can be employed to quantify entanglement in large quantum devices via efficient quantum tomography (Riofrío et al., 2017).
The new research field of quantum information and computation has emerged on the intersection between quantum physics, computer science and mathematics. Its main idea is to treat information on the basis of quantum mechanics so that computation and communication are done with essentially quantum elements. At present quantum information attracts enormous interest of scientific community becoming the priority research direction for many academic institution and private companies. Our research has focused on quantifying and tuning the Entanglement, teleportation using quantum dots, decoherence in spin systems and solid state implementations of qubits.
The ability to control the state of individual atoms is a new challenge for science and technology in the 21st century. Currently, experiments on individual quantum systems such as trapped ions, single molecules, quantum dots, superconducting qubits and photons are crucial for the rapidly growing field of quantum information processing and communication. In general, solid state systems are preferable for scaling and the choice of material plays a crucial role; for example, in classical electronic devices continual performance enhancement and miniaturization is strongly linked to the success of silicon-based technology. For quantum applications, diamond has the potential to become the material of choice, because its large bandgap enables the control of optically active impurities and higher operation temperature. This focus issue collates original research contributions from some of the leading groups in the field as a showcase for the very latest developments in diamond-based quantum technologies.
In order to provide novel techniques for processing, storing, and transmitting information, the multidisciplinary field of quantum information science (QIS) integrates ideas from quantum physics [ 4 ] with information science. However, due to a number of events, including Peter Shor’s invention of quantum algorithms and the rise in interest in quantum computing, the history of QIS started to expand quickly in the early to middle 1990s. Peter Shor, a physicist and mathematician, developed the first quantum algorithm that could factor big numbers exponentially more rapidly than any classical algorithm in 1994. This finding triggered strong interest in quantum computing’s potential to tackle issues that are currently unsolvable for classical computers. Since then, QIS has advanced due to the development of novel quantum algorithms and enhancements in the hardware used for quantum computing. Understanding complex quantum phenomena like entanglement and superposition and developing novel strategies for utilizing them for information processing and communication are the core goals of QIS. Quantum bits (qubits) can exist in superpositions of 0 and 1 simultaneously, which enables far more efficient computation than classical bits, which can only be in one state or the other at a given time. Superposition is a key concept in quantum computing. In addition to superposition, entanglement, coherence, and quantum algorithms are other important QIS concepts. Entanglement is a key feature of quantum mechanics and has been observed experimentally in a wide range of physical systems, including photons, atoms, and superconducting qubits. Two particles can get entangled with one another through a phenomenon called entanglement in which their quantum states exhibit a high correlation. This indicates that even if two particles are separated by a considerable distance, modifying the state of one can change the state of the other. No matter how far away two separate particles are from one another when they are entangled, measuring the state of one particle immediately gives the state of another particle. It plays a central role in many quantum technologies, including quantum computing for solving complex problems that take classical computers a long time to solve, quantum cryptography for secure communications, quantum sensing for quantum properties of particles to enable more precise measurements, and quantum networking to improve communication and processing speed over both short and long distances. Quantum metrology methods use the principles of quantum mechanics to improve the accuracy of measurements in fields like gravity sensors, timekeeping, and frequency standards. Some of the benefits of QIS are enhanced computing power, improved communication, advanced cryptography, more precise scientific measurements, and better logistics optimization.