Spontaneous decay of artificial atoms in a multi-qubit system

We consider a one-dimensional chain of N equidistantly spaced noninteracting qubits embedded in an open waveguide. In the frame of single-excitation subspace, we systematically study the evolution of qubits amplitudes if the only qubit in the chain was initially excited. We show that the temporal dynamics of qubits amplitudes crucially depend on the value of kd, where k is the wave vector, d is a distance between neighbor qubits. If kd is equal to an integer multiple of $\pi$, then the qubits are excited to a stationary level which scales as SN^{-1}S. We show that in this case, it is the dark states which prevent qubits from decaying to zero even though they do not contribute to the output spectrum of photon emission. For other values of kd the excitations of qubits have the form of damping oscillations, which represent the vacuum Rabi oscillations in a multi-qubit system. In this case, the output spectrum of photon radiation is defined by a subradiant state with the smallest width.Comment: 22 pages, 12 figures, 17 reference

Spontaneous decay of artificial atoms in a three-qubit system

We study the evolution of qubits amplitudes in a one-dimensional chain consisting of three equidistantly spaced noninteracting qubits embedded in an open waveguide. The study is performed in the frame of single-excitation subspace, where the only qubit in the chain is initially excited. We show that the dynamics of qubits amplitudes crucially depend on the value of $kd$, where $k$ is the wave vector, $d$ is a distance between neighbor qubits. If $kd$ is equal to an integer multiple of $\pi$, then the qubits are excited to a stationary level. In this case, it is the dark states which prevent qubits from decaying to zero even though they do not contribute to the output spectrum of photon emission. For other values of $kd$ the excitations of qubits exhibit the damping oscillations which represent the vacuum Rabi oscillations in a three-qubit system. In this case, the output spectrum of photon radiation is determined by a subradiant state which has the lowest decay rate. We also investigated the case with the frequency of a central qubit being different from that of the edge qubits. In this case, the qibits decay rates can be controlled by the frequency detuning between the central and the edge qubits.Comment: 18 pages, 13 figures, the reference list is updated. The text on pages 10 and 12 is updated. arXiv admin note: text overlap with arXiv:2104.0492

Quantum phase measurement for two-qubit states in an open waveguide

We present a new method for quantum state tomography within a single-excitation subspace of two-qubit states in an open waveguide. The system under investigation consists of three qubits in an open waveguide, separated by a distance comparable to the wavelength of the electromagnetic field. We show that the modulation of the frequency of the central ancillary qubit allows us to obtain unambiguous information about the initial phase difference $\varphi_1-\varphi_3$ of the edge qubits via the measurement of the evolution of their probability amplitudes.Comment: 10 pages, 4 figures, updated introduction and conclusio

Single-photon scattering on a qubit. Space-time structure of the scattered field

We study the space-time structure of the scattered field induced by the scattering of a single photon pulse on a qubit embedded in 1D open waveguide. We show that for large distance $x$ from qubit and at times $t$ long after the scattering event our theory for the reflected and transmitted amplitudes provides the result which is well known from the stationary scattering theories. However, in general, the structure of the scattered field is different from the stationary limit. This limit is obtained when both the distance from the qubit and the time that proceed after the scattering event tend to infinity. The approach to the stationary limit is very slow. The correction field decreases as the inverse powers of $x$ and $t$ as the distance from the qubit and the time after the interaction increase. Moreover, the scattered field contains the terms which depend only on the distance from the qubit, but not on the time. It means that as the distance is fixed the field corrections to the stationary limit remain unaltered no matter how long has passed since the beginning of the scattering event.Comment: 11 pages, 10 figure

Interaction Ultrasound Pulse with Ferromagnet Plate in Magnetoelastic Resonance Condition

Изучается рассеяние ультразвукового волнового пакета нормально падающего на поперечно на- магниченную ферромагнитную пластину в области магнитоупругого резонанса. За счет обра- зования связанных правополяризованных упругих и спиновых волн имеется серия нулей и полю- сов в спектре амплитуд отражения и прохождения. Показано, что за эволюцию волнового поля ответственны два типа полюсов амплитуд рассеяния. В тонких пластинах можно возбудить квазистационарные состояния, связанные с квазиспинволновыми полюсами, в более толстых пла- стинах усиливается роль квазиакустических полюсов. Рассчитываются форма и времена жизни вторичных волновых структур.The scattering of ultrasound wave packet which normally falls on ferromagnetic plate near of magne- toelastic resonance is studied. The spectra of reflection and transmission amplitude contain zeros and poles connected with elastic and spin clockwised polarized waves coupling. Two types of zeros and poles responsibles for evolution of wave field. The quasistationary state connected with quasispin wave poles can be induced in the thin plates. The role of quasiacoustic wave poles arise in the thick plates. The decay times and form are calculated

Interaction Ultrasound Pulse with Ferromagnet Plate in Magnetoelastic Resonance Condition

Изучается рассеяние ультразвукового волнового пакета нормально падающего на поперечно на- магниченную ферромагнитную пластину в области магнитоупругого резонанса. За счет обра- зования связанных правополяризованных упругих и спиновых волн имеется серия нулей и полю- сов в спектре амплитуд отражения и прохождения. Показано, что за эволюцию волнового поля ответственны два типа полюсов амплитуд рассеяния. В тонких пластинах можно возбудить квазистационарные состояния, связанные с квазиспинволновыми полюсами, в более толстых пла- стинах усиливается роль квазиакустических полюсов. Рассчитываются форма и времена жизни вторичных волновых структур.The scattering of ultrasound wave packet which normally falls on ferromagnetic plate near of magne- toelastic resonance is studied. The spectra of reflection and transmission amplitude contain zeros and poles connected with elastic and spin clockwised polarized waves coupling. Two types of zeros and poles responsibles for evolution of wave field. The quasistationary state connected with quasispin wave poles can be induced in the thin plates. The role of quasiacoustic wave poles arise in the thick plates. The decay times and form are calculated