The basic assumption underlying various quantum information technologies, such as quantum computation and quantum communication, is that qubits are physical objects. However, this assumption is false. A qubit is a quantum superposition, which is a purely mathematical entity in a Hilbert space for description of a two-level quantum system. There is no theoretical or experimental evidence for quantum superpositions in general, and for qubits in particular, having physical counterparts in the real world, although quantum systems themselves are all physical objects. Nevertheless, quantum superpositions failing to be physical objects does not necessarily imply quantum mechanics failing to be correct. Hilbert spaces differ essentially from the three-dimensional Euclidean space; the latter is the model of space in which we live and measure physical quantities. Associated with time or space coordinates, measurements of all quantum systems must be performed in the real world. However, precise time and space coordinates are not attainable by measurement. Based on a comparison between the Euclidean space and Hilbert spaces, this paper shows that no quantum systems in the real world can realize qubits, and hence, quantum information technologies are not physically realizable; their so-called advantages over classical information technologies make little sense.
The basic assumption underlying various quantum information technologies, such as quantum computation and quantum communication, is that qubits are physical objects. However, this assumption is false. A qubit is a quantum superposition, which is a purely mathematical entity in a Hilbert space for description of a two-level quantum system. There is no theoretical or experimental evidence for quantum superpositions in general, and for qubits in particular, having physical counterparts in the real world, although quantum systems themselves are all physical objects. Nevertheless, quantum superpositions failing to be physical objects does not necessarily imply quantum mechanics failing to be correct. Hilbert spaces differ essentially from the three-dimensional Euclidean space; the latter is the model of space in which we live and measure physical quantities. Associated with time or space coordinates, measurements of all quantum systems must be performed in the real world. However, precise time and space coordinates are not attainable by measurement. Based on a comparison between the Euclidean space and Hilbert spaces, this paper shows that no quantum systems in the real world can realize qubits, and hence, quantum information technologies are not physically realizable; their so-called advantages over classical information technologies make little sense.
Nowadays quantum information science is in a state of theoretic completeness; much is invested to research quality physical solution for quantum computer and applications, so the field is led by physicists and information science and technology professionals. This field proved its potential and many (including us) believe it is in the right direction to go. In this paper we'll try to present and analyze the philosophy and nature of quantum information science and discuss hot topics around them. Although there is plenty of space for discussion around this field, we will concentrate on some important issues, such as quantum communication, algorithms and cryptography. Communication promises to be one of the directions where huge breakthroughs will be observed (entanglement as communication), algorithms have already shown exponential advantage (Shor's factoring) over classical counterparts and different paradigm of information processing. Cryptography seems to utilize general achievements in quantum information science and make encryption protocols very secure. Quantum computation can be understood as a generalization of classical computation: The possible states of a quantum computer are superpositions of bit strings, where the tensor factor is called a quantum bit or qubit. To evaluate the computational complexity of an algorithm, either classical or quantum, it is necessary to specify a set of elementary operations, the number of which used during the computation quantities the complexity. If we allow arbitrary permutations classically, or arbitrary unitary transformations quantum mechanically, any state can be reached from any other state in a single step. The general kind of quantum computer should be programmed to perform distinctively quantum operations such as generating two bits in a superposition state. An appropriate measurement on the final superposed state of the computer produces a probabilistic behavior of the output, and because of this quantum parallelization does not reduce the average time required for parallelizable computation completion. The development of quantum computing science and technology as well as quantum computers as thinking machines is very dependent on different achievements of modern research in fundamental and applied physics as well as novel mathematical methods and tools.
Bell’s inequality is derived by resorting to a hidden-variable theory devised for resolving the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. The legitimacy of quantum superposition for describing the physical world is the essence of the debate. Einstein argued against the legitimacy of quantum superposition. Testing Bell’s inequality by experiments with the experimental result explained by Bell’s theorem opened the door to so-called quantum information technologies. In quantum information theory, “quantum bit” (or “qubit” for short) in a form of quantum superposition is supposed to carry quantum information. In the present paper, a new principle, the general principle of measurements, has been proved as a mathematical theorem. Based on this principle, the experiment for testing Bell’s inequality and so-called experimental evidence for physically realizable “qubit” have been scrutinized. The findings are as follows. Although most physicists believe that Einstein’s vision of the physical world contradicts the experimental result of testing Bell’s inequality, neither the experimental result nor Bell’s theorem is relevant to Einstein’s viewpoint, because Bell’s inequality failed to capture the essence of the Einstein-Bohr debate. The experimental result and the measurement outcomes of various experiments involving “qubit” are all erroneously explained. Quantum mechanics can be completed by using disjunction (“or”) as the logical relation between the orthonormal vectors that span an arbitrarily given Hilbert space without resorting to any hidden-variable theory, while the mathematical setting will remain essentially unchanged. All kinds of “qubit” violate the general principle of measurements and can only describe imaginary objects that do not exist in the real world. A very regrettable conclusion from the above findings is inevitable: All quantum information technologies are not physically realizable, because quantum information has no physical carriers.
In this section we provide a broad overview of the basic principles of quantum mechanics and how they enable modern quantum technologies. The starting point is the concept of superposition, which allows quantum systems to be in multiple states at the same time and forms the basis of quantum computation using qubits and parallel processing of information. The conversation then turns to quantum entanglement, a non-classical effect that creates strong correlations between particles, and has applications in secure communication and quantum teleportation. Also mentioned is the quantum coherence, which preserves phase relations between quantum states and makes it possible for quantum systems to function correctly. But it is also emphasized that quantum coherence is fragile to environmental perturbations. This chapter also covers quantum measurement, taking into account the probabilistic nature of quantum mechanics, and how the act of observation results in the collapse of a quantum state to a definite outcome. These principles together constitute the theoretical basis of quantum computing, where quantum gates and algorithms and qubits take advantage of superposition, entanglement and interference to offer computational benefits over classical systems. The most important algorithms like Shor’s and Grover’s algorithms that demonstrate a considerable speed-up in solving the problem are discussed along with different models of quantum computing, such as gate, adiabatic and measurement-based models. Furthermore, the section reviews some physical realizations of quantum systems, such as superconducting qubits, trapped ions, photonic systems and topological qubits, with their advantages and difficulties. Overall, this discussion shows how the basic principles of quantum mechanics are the foundation for the development of advanced quantum technologies, while also dealing with the practical difficulties that arise in their implementation.
Bell’s inequality is derived by resorting to a hidden-variable theory devised for resolving the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. The legitimacy of quantum superposition for describing the physical world is the essence of the debate. Einstein argued against the legitimacy of quantum superposition. Testing Bell’s inequality by experiments with the experimental results explained by Bell’s theorem opened the door to so-called quantum information technologies. In quantum information theory, “quantum bit” (or “qubit” for short) in a form of quantum superposition is supposed to represent quantum information. In the present paper, a new principle, the general principle of measurements, is introduced and proved as a mathematical theorem. Based on this principle, the experiments for testing Bell’s inequality and so-called experimental evidence for physically realizable “qubit” are scrutinized. The findings are as follows. Although most physicists believe that Einstein’s vision of the physical world contradicts the experimental results of testing Bell’s inequality, actually Einstein’s viewpoint is irrelevant to Bell’s theorem. Bell’s inequality failed to capture the essence of the Einstein-Bohr debate. The experimental results of testing Bell’s inequality and the measurement outcomes of various experiments involving “qubit” are all erroneously explained. Without involving hidden variables, quantum mechanics can be completed based on the general principle of measurements by using disjunction (“or”) as the logical relation between the orthonormal vectors that span an arbitrarily given Hilbert space, and the mathematical setting can remain essentially unchanged. All kinds of “qubit” violate the general principle of measurements and can only describe imaginary objects that do not exist in the real world. A very regrettable conclusion from the above findings is inevitable: Quantum information has no physical carriers, and all quantum information technologies are not physically realizable.
As we have seen, even a single qubit is a surprisingly interesting object. However, the real power of quantum information processing begins with systems of two or more qubits. Before studying these in detail we need to expand our notation a little. Consider a system of two qubits, labeled a and b , each of which has two basis states, |0⧽ and |1⧽. The whole system then has four basis states, which can be written as |0 a 0 b ⧽, |0 a 1 b ⧽, |1 a 0 b ⧽ and |1 a 1 b ⧽, and can be found in any general superposition of these states, so that it occupies a four-dimensional Hilbert space. In the same way, a system of three qubits inhabits an eight-dimensional Hilbert space, and so on. This exponential increase in the size of the Hilbert space with a linear increase in the number of qubits underlies the power of quantum computers. Direct products The size of the Hilbert spaces involved can also be a huge problem, however, making it difficult to describe states of systems with many qubits. A partial solution is to note that some states can be described in a simpler way, using the concept of direct products . These states, in which the individual qubits can in principle be discussed separately, make up a tiny minority of the states accessible to a multi-qubit system, but include many important states, most notably the basis states. States of this kind are said to be separable , and states which are not separable are said to be entangled . Entangled states are much more interesting than separable ones, but it is wise to begin with the simpler case.
Bell’s inequality is derived by resorting to a hidden-variable theory devised for resolving the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. The legitimacy of quantum superposition for describing the physical world is the essence of the debate. Einstein argued against the legitimacy of quantum superposition. Testing Bell’s inequality by experiments with the experimental results explained by Bell’s theorem opened the door to so-called quantum information technologies. In quantum information theory, “quantum bit” (or “qubit” for short) in a form of quantum superposition is supposed to represent quantum information. In the present paper, a new principle, the general principle of measurements, is introduced and proved as a mathematical theorem. Based on this principle, the experiments for testing Bell’s inequality and so-called experimental evidence for physically realizable “qubit” are scrutinized. The findings are as follows. Although most physicists believe that Einstein’s vision of the physical world contradicts the experimental results of testing Bell’s inequality, actually Einstein’s viewpoint is irrelevant to Bell’s theorem. Bell’s inequality failed to capture the essence of the Einstein-Bohr debate. The experimental results of testing Bell’s inequality and the measurement outcomes of various experiments involving “qubit” are all erroneously explained. Without involving hidden variables, quantum mechanics can be completed based on the general principle of measurements by using disjunction (“or”) as the logical relation between the orthonormal vectors that span an arbitrarily given Hilbert space, and the mathematical setting can remain essentially unchanged. All kinds of “qubit” violate the general principle of measurements and can only describe imaginary objects that do not exist in the real world. A very regrettable conclusion from the above findings is inevitable: Quantum information has no physical carriers, and all quantum information technologies are not physically realizable.