In space situational awareness scenarios, the objects needed to be characterized and identified are usually quite far away and quite dim. Thus, optical detectors need to be able to sense these very dim optical signals. Quantum interference in a three-level system can lead to amplification of optical signals. If we put a three-level system into a cavity tuned to the frequency of an incoming optical signal, we anticipate the amplification possibilities should be increased proportional to the quality factor of the cavity. Our vision is to utilize quantum dots in photonic crystal cavities, but as a stepping stone we first investigate a simple three-level system in a free-space optical cavity. We investigate quantum interference and classical interference effects when a three-level system interacts with both a cavity field mode and an external driving field mode. We find that under certain circumstances the cavity field evolves to be equal in magnitude to, but 180° out-of-phase with the external pump field when the pump field frequency equals the cavity frequency. At this point the resonance fluorescence from the atom in the cavity goes to zero due to a purely classical interference effect between the two out-of-phase fields. This is quite different from the quantum interference that occurs under the right circumstances, when the state populations are coherently driven into a linear combination that is decoupled from any applied field - and population is trapped in the excited states, thus allowing for a population inversion and an amplification of incoming optical signals.
In space situational awareness scenarios, the objects needed to be characterized and identified are usually quite far away and quite dim. Thus, optical detectors need to be able to sense these very dim optical signals. Quantum interference in a three-level system can lead to amplification of optical signals. If we put a three-level system into a cavity tuned to the frequency of an incoming optical signal, we anticipate the amplification possibilities should be increased proportional to the quality factor of the cavity. Our vision is to utilize quantum dots in photonic crystal cavities, but as a stepping stone we first investigate a simple three-level system in a free-space optical cavity. We investigate quantum interference and classical interference effects when a three-level system interacts with both a cavity field mode and an external driving field mode. We find that under certain circumstances the cavity field evolves to be equal in magnitude to, but 180° out-of-phase with the external pump field when the pump field frequency equals the cavity frequency. At this point the resonance fluorescence from the atom in the cavity goes to zero due to a purely classical interference effect between the two out-of-phase fields. This is quite different from the quantum interference that occurs under the right circumstances, when the state populations are coherently driven into a linear combination that is decoupled from any applied field - and population is trapped in the excited states, thus allowing for a population inversion and an amplification of incoming optical signals.
We investigate quantum interference and classical interference effects when a three-level system interacts with both a cavity field mode and an external driving field mode, within the confines of a photonic crystal material. In freespace, we found that under certain circumstances the cavity field evolves to be equal in magnitude to, but 180° out-of- phase with the external pump field when the pump field frequency equals the cavity frequency. The better the cavity, the quicker this build-up occurs. When the cavity field reaches this out-of-phase condition, the resonance fluorescence from the atom in the cavity goes to zero. This is a purely classical interference effect between the two out-of-phase fields, with the resonance fluorescence going to zero at the same time as the two excited state populations go to zero. This is quite different from the quantum interference that occurs under the right circumstances, when the state populations are coherently driven into a linear combination that is decoupled from any applied field - and population is trapped in the excited states, thus allowing for a population inversion and an amplification of incoming optical signals. In this paper, we investigate the additional effects due to the presence of the altered photon density of states in a photonic crystal.
We investigate quantum interference and classical-interference effects when three-level atoms in the ``$\ensuremath{\Lambda}$'' or ``V'' configuration interact with both a cavity-field mode and an external driving field mode. We describe electromagnetically induced transparency ($\ensuremath{\Lambda}$ configuration), as well as a ``field-induced transparency'' (V configuration), and we go beyond the weak cavity-field studies of previous papers by utilizing a Heisenberg-picture density matrix approach. We find that under certain circumstances the cavity field evolves to be equal in magnitude to, but $180\ifmmode^\circ\else\textdegree\fi{}$ out of phase with, the external pump field when the pump-field frequency equals the cavity frequency, a surprising effect found in two-level atoms in a cavity excited by an external pump field that persists in three-level atoms. The better the cavity, the quicker this buildup occurs. When the cavity field reaches this ``out-of-phase'' condition, the resonance fluorescence from the atom in the cavity goes to zero. This is a purely classical-interference effect between the two out-of-phase fields, with the resonance fluorescence going to zero at the same time as the two excited state populations go to zero. This is quite different from the quantum interference that occurs under the right circumstances when the state populations are coherently driven into a linear combination that is decoupled from any applied field and population is trapped in the excited states (``coherent population trapping''). When the cavity frequency is tuned to the frequency at which quantum interference would occur, the two interference effects compete with each other. The cavity field begins to evolve toward the $180\ifmmode^\circ\else\textdegree\fi{}$ out-of-phase condition, thereby approaching a classical destructive interference condition with the pump field. Then at some point before 100% classical interference occurs, depending on the cavity damping rate and atom/cavity coupling strength, the atom builds up its coherence between state populations to produce the quantum interference effect. At that point, the atom becomes transparent and resonance fluorescence disappears, including fluorescence into the cavity, thereby causing the cavity field to die away.
I theoretically demonstrate all-optical modulation and amplification in a one-dimensional photonic-crystal (PC) cavity with a large number of two-level quantum dots (QD's). Populations in the ground and excited states of two-level QD's with large transition dipole moments are greatly changed by an external laser, and this affects the electrical susceptibility of the QD's. In other words, all-optical modulation, in which light (the signal light) is modulated by light (the external laser), becomes possible. Moreover, a large contrast of the electromagnetic local densities of states in the PC cavity enables steady-state population inversion in two-level systems, which is generally considered impossible. The output signal power is more than twice as large as the input power at certain frequencies.
This thesis examines the effect of quantum interference occuring in a three-level atom in the V-configuration, on a variety of optical effects such as controlled spontaneous emission, population trapping, lasing without population inversion, controlled field intensity and photon statistics. Calculations are carried out numerically via the master equation approach and analytically using dressed atom analysis. Various atom-laser coupling configurations are investigated and dressed states identified in each case. The system is shown to exhibit trapping states for a variety of atom-laser coupling configurations. Moreover, the thesis focuses on the effect of quantum interference on a cavity QED system. Three different cavity detunings with respect to the entangled atom-laser system are considered. It is shown in each case how the singly dressed entangled system interacts with the cavity field to form entangled doubly dressed structures. Again, the system is shown to exhibit population trapping states with dependence on the cavity damping rate in one of the detunings considered. In addition, photon statistics of the cavity field are calculated and shown to be sensitive to the degree of quantum interference. Interestingly, controlled field intensity and sub-Poissonian statistics are obtained for certain parameters of the two off-resonance cases considered
Non-classical properties and quantum interference (QI) in two-photon excitation of
a three level atom (|1〉), |2〉, |3〉) in a ladder configuration, illuminated by multiple
fields in non-classical (squeezed) and/or classical (coherent) states, is studied. Fundamentally
new effects associated with quantum correlations in the squeezed fields
and QI due to multiple excitation pathways have been observed. Theoretical studies
and extrapolations of these findings have revealed possible applications which are
far beyond any current capabilities, including ultrafast nonlinear mixing, ultrafast
homodyne detection and frequency metrology. The atom used throughout the experiments
was Cesium, which was magneto-optically trapped in a vapor cell to produce
a Doppler-free sample. For the first part of the work the |1〉 → |2〉 → |3〉 transition
(corresponding to the 6S1/2F = 4 → 6P3/2F' = 5 → 6D5/2F = 6 transition) was
excited by using the quantum-correlated signal (Ɛs) and idler (Ɛi) output fields of a
subthreshold non-degenerate optical parametric oscillator, which was tuned so that
the signal and idler fields were resonant with the |1〉 → |2〉 and |2〉 → |3〉 transitions,
respectively. In contrast to excitation with classical fields for which the excitation
rate as a function of intensity has always an exponent greater than or equal to two,
excitation with squeezed-fields has been theoretically predicted to have an exponent
that approaches unity for small enough intensities. This was verified experimentally
by probing the exponent down to a slope of 1.3, demonstrating for the first time a
purely non-classical effect associated with the interaction of squeezed fields and atoms.
In the second part excitation of the two-photon transition by three phase coherent
fields Ɛ1 , Ɛ2 and Ɛ0, resonant with the dipole |1〉 → |2〉 and |2〉 → |3〉 and quadrupole
|1〉 → |3〉 transitions, respectively, is studied. QI in the excited state population is
observed due to two alternative excitation pathways. This is equivalent to nonlinear
mixing of the three excitation fields by the atom. Realizing that in the experiment
the three fields are spaced in frequency over a range of 25 THz, and extending this
scheme to other energy triplets and atoms, leads to the discovery that ranges up to
100's of THz can be bridged in a single mixing step. Motivated by these results,
a master equation model has been developed for the system and its properties have
been extensively studied.