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qubits
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frequencies... frequencies.... frequency... network of stochastic oscillators... QUBIT... frequencies);
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Since the dawn of quantum information science, laser-cooled trapped atomic ions have been one of the most compelling systems for the physical realization of a quantum computer. By applying qubit state dependent forces to the ions, their collective motional modes can be used as a bus to realize entangling quantum gates. Ultrafast state-dependent kicks [1] can provide a universal set of quantum logic operations, in conjunction with ultrafast single qubit rotations [2], which uses only ultrafast laser pulses. This may present a clearer route to scaling a trapped ion processor [3]. In addition to the role that spin-dependent kicks (SDKs) play in quantum computation, their utility in fundamental quantum mechanics research is also apparent. In this thesis, we present a set of experiments which demonstrate some of the principle properties of SDKs including ion motion independence (we demonstrate single ion thermometry from the ground state to near room temperature and the largest Schrodinger cat state ever created in an oscillator), high speed operations (compared with conventional atom-laser interactions), and multi-qubit entanglement operations with speed that is not fundamentally limited by the trap oscillation frequency. We also present a method to provide higher stability in the radial mode ion oscillation frequencies of a linear radiofrequency (rf) Paul trap--a crucial factor when performing operations on the rf-sensitive modes. Finally, we present the highest atomic position sensitivity measurement of an isolated atom to date of ~0.5 nm Hz^(-1/2) with a minimum uncertainty of 1.7 nm using a 0.6 numerical aperature (NA) lens system, along with a method to correct aberrations and a direct position measurement of ion micromotion (the inherent oscillations of an ion trapped in an oscillating rf field). This development could be used to directly image atom motion in the quantum regime, along with sensing forces at the yoctonewton [10^(-24) N)] scale for gravity sensing, and 3D imaging of atoms from static to higher frequency motion. These ultrafast atomic qubit manipulation tools demonstrate inherent advantages over conventional techniques, offering a fundamentally distinct regime of control and speed not previously achievable.
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6-The electron oscillating period as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... Fig.4. A-Function relationship between the first excited state energy and the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-Function relationship between the first excited energy and the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-Function relationship between the first excited energy and the temperature and the confinement length for different cyclotron frequencies and ,,,; D-Function relationship between the first excited energy and of the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,... Fig.1. A-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different electron-phonon coupling constants and ,,, ; B-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different electric field strengths and ,,,; C-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different confinement lengths and ,,,; D-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different Coulomb impurity potentials and ,,,... Fig.6. A-The electron oscillation period as functions of the temperature and the cyclotron frequency for different electron-phonon coupling constants and ,,,; B-The electron oscillation period as functions of the temperature and the cyclotron frequency for different electric field strengths and,,,; C-The electron oscillation period as functions of the temperature and the cyclotron frequency for different confinement lengths and ,,,; D-The electron oscillation period as functions of the temperature and the cyclotron frequency for different Coulomb impurity potentials and ,,,... 7-The electron oscillating period as functions of the temperature and the electron-phonon coupling constant and etc. in triangular quantum dot qubit under an electric field.docx... 2-The first excited state energy as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... 3-The ground state energy as functions of the temperature and the electron-phonon coupling constant and etc. in triangular quantum dot qubit under an electric field.docx... Fig.7. A-The electron oscillation period as functions of the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-The electron oscillation period as functions of the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-The electron oscillation period as functions of the temperature and the confinement length for different cyclotron frequencies and ,,,; D-The electron oscillation period as functions of the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,... 1-The ground state energy as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... Fig.3. A-Function relationship between the ground state energy and the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-Function relationship between the ground state energy and the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-Function relationship between the ground state energy and of the temperature and the confinement length for different cyclotron frequencies and ,,,; D-Function relationship between the ground state energy and the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,
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Superconducting qubits
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While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven Bloch vector dynamics of a single exciton confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.
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While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven Bloch vector dynamics of a single exciton confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.
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In optically controlled quantum computers it may be favorable to address different qubits using light with different frequencies, since the optical diffraction does not then limit the distance between qubits. Using qubits that are close to each other enables qubit-qubit interactions and gate operations that are strong and fast in comparison to qubit-environment interactions and decoherence rates. However, as qubits are addressed in frequency space, great care has to be taken when designing the laser pulses, so that they perform the desired operation on one qubit, without affecting other qubits. Complex hyperbolic secant pulses have theoretically been shown to be excellent for such frequency-addressed quantum computing [I. Roos and K. Molmer, Phys. Rev. A 69, 022321 (2004)]—e.g., for use in quantum computers based on optical interactions in rare-earth-metal-ion-doped crystals. The optical transition lines of the rare-earth-metal-ions are inhomogeneously broadened and therefore the frequency of the excitation pulses can be used to selectively address qubit ions that are spatially separated by a distance much less than a wavelength. Here, frequency-selective transfer of qubit ions between qubit states using complex hyperbolic secant pulses is experimentally demonstrated. Transfer efficiencies better than 90% were obtained. Using the complex hyperbolic secant pulses it was also possible to create two groups of ions, absorbing at specific frequencies, where 85% of the ions at one of the frequencies was shifted out of resonance with the field when ions in the other frequency group were excited. This procedure of selecting interacting ions, called qubit distillation, was carried out in preparation for two-qubit gate operations in the rare-earth-metal-ion-doped crystals. The techniques for frequency-selective state-to-state transfer developed here may be also useful also for other quantum optics and quantum information experiments in these long-coherence-time solid-state systems.
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We implement distinct quantum gates in parallel on two entangled frequency-bin qubits for the first time. Our basic quantum operation controls the spectral overlap between adjacent frequency bins, allowing us to observe frequency-bin Hong-Ou-Mandel interference with a visibility of 0.971±0.007, a record for two photons of different colors. By integrating this tunability with frequency parallelization, we synthesize independent gates on entangled qubits in the same optical fiber and flip their spectral correlations. The ultralow noise of our gates preserves entanglement purity, as evidenced by a 9.8σ violation of an entropic separability bound. Our results constitute the first closed, user-defined gates on frequency-bin qubits in parallel, with application to the development of frequency-based quantum information processing.
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We implement distinct quantum gates in parallel on two entangled frequency-bin qubits for the first time. Our basic quantum operation controls the spectral overlap between adjacent frequency bins, allowing us to observe frequency-bin Hong-Ou-Mandel interference with a visibility of 0.971±0.007, a record for two photons of different colors. By integrating this tunability with frequency parallelization, we synthesize independent gates on entangled qubits in the same optical fiber and flip their spectral correlations. The ultralow noise of our gates preserves entanglement purity, as evidenced by a 9.8σ violation of an entropic separability bound. Our results constitute the first closed, user-defined gates on frequency-bin qubits in parallel, with application to the development of frequency-based quantum information processing.
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