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Electromagnetically Induced Transparency in Semiconductor Quantum Wells
Published in Kong-Thon Tsen, and Nanostructures, 2018
Future progress in the manipulation of quantum coherences in semiconductors will certainly benefit from systems with smaller decoherence rates. Semiconductor quantum dot systems can have decoherence times for dipole transitions of hundreds of picosecond,52,53 and the effects of exciton-exciton scattering are expected to be greatly reduced. Experiments showing coherent manipulation of dipole coherence in the form of Rabi oscillations54–56 are a natural progression toward realizing quantum interference effects such as EIT. While the quantum dot system is conceptually more atomic-like than the quantum well system, theoretical treatments of EIT in quantum dots show that many-body interactions cannot be ignored.57 Further study is also needed to explore the properties of nonradiative coherences in quantum dots.
Quantum Computer
Published in Shabnam Siddiqui, Quantum Mechanics, 2018
The wavefunction of a quantum system has complete information about the system and is described as a linear superposition of many quantum states. However, when a measurement is performed to determine the state of the system, it collapses the superposition state into one of the possible states. Thus, complete information about the system cannot be obtained. This behavior of quantum mechanics has puzzled scientists for several decades and is commonly referred to as a “measurement problem.” Several scientists have attempted to explain such behavior theoretically. The very first and widely accepted explanation was provided by the “Copenhagen interpretation” (as discussed in Chapters 3 and 7). This interpretation was formulated by Neils Bohr (1928) and his co-workers. According to this interpretation, quantum systems do not actually exist in a definite state before the measurement, and the act of measurement causes the superposition state to collapse to a single state. In simple words, “quantum systems behave in this way because that is the way they are.” It cannot explain what occurs in the measurement process that causes such a collapse of the wavefunction. There is another explanation known as “Many worlds Interpretation” which tries to describe the whole universe using a wavefunction. It was formulated by Hugh Everett III (1957). At present, it is not a widely accepted theory. Many scientists believe that this theory is inconsistent. The third theory that tries to explain the measurement process, is called the “Decoherence theory” and it is a relatively a new one. It is most useful in the field of quantum computation and quantum information. The foundation of this theory was laid by H. D Zeh, and W. D Zurek (1980). According to this theory, a quantum system interacts with its environment. The interaction between the quantum system and the environment causes it to lose information to the environment. This loss of information by the quantum system is referred to as decoherence. This also means loss of quantum coherence. It is an irreversible process, and once the information is lost, it cannot be recovered. The decoherence theory provides an explanation of the collapse of the wavefunction. For the last two decades this theory has become an important tool for the development of a reliable quantum computer.
Counteracting quantum decoherence with optimized disorder in discrete-time quantum walks
Published in Journal of Modern Optics, 2019
Quantum state decoherence occurs as the wavefunction of a quantum system is collapsed, either entirely or partially, by energy dissipation into the environment or by the disclosure of its state information. Typical examples of quantum decoherence include the spontaneous decay in two-level systems and the scattering loss during the propagation of entangled photons (1). On the other hand, disorder describes the disturbance of the system's wavefunction by the chaotic external degrees of freedom it is coupled to, such as inhomogeneous chemical potential in a photosynthetic network (2). While corresponding to different mechanisms, both decoherence and disorder deteriorate the performance of quantum systems. In light of their prevalence in practice, there have been extensive efforts to address each of them, e.g. by applying high magnetic fields and error correction (3,4).
Stationary quantum correlation and coherence of two-mode Kerr nonlinear coupler interdicting with Su(2)-system under intrinsic damping
Published in Journal of Modern Optics, 2018
The effect of the intrinsic decoherence on the negativity is reported in Figure 3(b) with the same parameters as of Figure 3(b), but for . We see that the intrinsic decoherence leads to the deterioration of the generated entanglement, where the negativity loses its regularity, and both of its amplitudes and frequencies decrease. In particular, we find that the negativity for the case of presents sudden death (51,52) and sudden birth (53,54) phenomena. In Figure 3(b), the entanglement between the Su and Su systems is enhanced by increasing the detuning.