Research
Precision quantum optics in the spatial domain
Resonant interferometric lithography beyond the diffraction limit
Schematic setup with standing wave writing fields incident on the photo resist, and with the position dependent medium response. The fringe pattern has sub-diffraction limit resolution. The solid blue line is the result without ground state decoherence, while the dotted lines are plotted for decoherence of the dark state with a large rate equal to five times the spontaneous decay rate of the dipole-allowed transitions. The two curves virtually coincide, demonstrating that our scheme is insensitive to large decoherence.
A fundamental limit to the spatial resolution of the interferometric lithography with classical uncorrelated light arises due to diffraction. To overcome this limit, several schemes have been proposed to improve the spatial resolution of interferometric lithography beyond the diffraction limit. These schemes are based on an N-photon absorption process and achieve a spatial resolution of λ/(2N), where λ is the wavelength of the light. The indispensable requirement of a multiphoton transition, however, is accompanied by the need for high light field intensities which makes an experimental realization of these schemes impractical.
We have found a novel approach for the generation of subwavelength structures in interferometric optical lithography which only comprises resonant atom-field interactions, such that no multiphoton absorber is required. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at arbitrarily low laser intensities.
In an alternative parameter range, our setup allows to write high-resolution images point by point over a range of order of the wavelengh ("needle operation").
We have found a novel approach for the generation of subwavelength structures in interferometric optical lithography which only comprises resonant atom-field interactions, such that no multiphoton absorber is required. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at arbitrarily low laser intensities.
In an alternative parameter range, our setup allows to write high-resolution images point by point over a range of order of the wavelengh ("needle operation").
Atom localization via multiple simultaneous quadrature measurements
Schematic setup of atoms flying through two perpendicular standing wave fields. The atom is coupled to the two cavity fields in the dispersive limit and imprints position-dependent phase shifts on the cavity fields. This allows to obtain two-dimensional position information simultaneously.
Precision measurement of the position of quantum particles is a long standing problem ever since the famous Heisenberg microscope. In order to improve current localization schemes, we have discusses localization and center-of-mass wavefunction measurement of a quantum particle using multiple simultaneous dispersive interactions of the particle with different standing wave fields. In particular, we have considered objects with an internal structure consisting of a single ground state and several excited states. The transitions between ground and the respective excited states are coupled to the light fields in the dispersive limit, thus giving rise to a phase shift of the light field during the interaction.
As main result, we could show that multiple simultaneous measurements allow both to increase the measurement or localization precision in a single direction and to perform multi-dimensional measurements or localization. Also, they may relax the experimental requirements for each individual measurement.
As main result, we could show that multiple simultaneous measurements allow both to increase the measurement or localization precision in a single direction and to perform multi-dimensional measurements or localization. Also, they may relax the experimental requirements for each individual measurement.
Measurement of the separation between atoms beyond diffraction limit
A possible experimental setup. Two nearby atoms are placed in a standing wave laser field. The fluorescence light emitted by the atoms and detected relying entirely on far-field methods allows to measure the interparticle distance over a broad range of sub-wavelength distances.
Precision measurement of small separations between two atoms or molecules has been of interest since the early days of science. Here, we discuss a scheme which yields spatial information on a system of two identical atoms placed in a standing wave laser field (see figure). The information is extracted from the collective resonance fluorescence spectrum, relying entirely on far-field imaging techniques. Both the interatomic separation and the positions of the two particles can be measured with fractional-wavelength precision over a wide range of distances from about λ/550 to λ/2. Similar results can also be obtained from the intensity-intensity correlation spectrum of the scattered light.
Localization of atomic ensembles via superfluorescence
Operation principle of scanning-dip spectroscopy. An atomic ensemble is driven by a standing wave field, and the intensity of the scattered light is measured. Then, the phase of the standing wave field is modified until no light is scattered. Since due to many-particle effects the spatial width of the intensity dip can be made very small, this provides a precise position measurement for the ensemble. Alternatively, properties such as width or particle number in the ensemble can be estimated.
Most effort in spatial precision measurements in quantum optics focusses on single quantum objects. We generalized these ideas to obtain sub-wavelength localization of an ensemble of atoms concentrated to a small volume in space. The ensemble is driven by a near-resonant standing wave light field. Our observable is the light scattered in the interaction of the atoms with a standing wave laser field. The fluorescence light can be described by an intensity profile, which depends on the standing wave field parameters, the ensemble properties, and which is modified due to collective effects in the ensemble of nearby particles. We demonstrated that the intensity profile can be tailored to suit different localization setups, and discussed two localization schemes. First, we showed how to localize an ensemble fixed at a certain position in the standing wave field. Second, we discussed localization of an ensemble passing through the standing wave field.