Raytheon BBN Technologies

Superconducting Qubit Systems

Raytheon BBN has been developing and experimenting with superconducting qubits with a systems perspective. We are interested in all aspects of quantum computing systems which include systems control as well as coupled qubit design and measurement. Raytheon BBN researchers have been some of the first to realize superconducting rapid single flux quantum (RSFQ) logic and superconducting monolithic microwave integrated circuits (SMMIC) for monolithic control of qubit systems at 10mK. In addition, we are advancing the state-of-the-art in room temperature control electronics with high-precision, low-noise, and scalable control systems. In Raytheon BBN’s 10mK dilution refrigerator, Raytheon BBN has demonstrated coherent control of a superconducting qubits with results that are consistent with the state-of-the-art. Here, we are experimenting with various qubit types with a focus on understanding the characteristics of each design approach and their respective advantages towards quantum computing.

Electromagnetically Induced Transparency (EIT) Experiments

Raytheon BBN achieved a breakthrough in the field of superconducting quantum circuits with the first observation of Coherent Population Trapping (CPT). CPT is closely related to Electromagnetically Induced Transparency (EIT), and both CPT and EIT are clear demonstrations of quantum interference due to coherence in multi-level quantum systems. In atomic systems, EIT has been shown to be a key ingredient in "slow light" propagation (at ~1 m/s), low light level coherent nonlinear optics, and quantum memories. In our experiment, we demonstrated CPT in a completely new system (superconducting quantum circuits) and in a completely new regime of the electromagnetic spectrum (microwave as opposed to optical). We observed CPT in a superconducting phase qubit by utilizing the three lowest lying levels of a local minimum of the phase qubit and simultaneously driving two coherent microwave transitions. We observed 58% suppression of excited state population under conditions of two-photon resonance, where EIT and CPT are expected to occur. Comparison and analysis with theoretical modeling clearly demonstrates that this degree of suppression requires macroscopic quantum interference. Furthermore, we showed that such a system could be used to measure dephasing times by using the observed time dependence of the excited state population. Future work in this direction will enable new paradigms for coherent nonlinear optics in the microwave regime and quantum processing in superconducting systems. This experiment was conducted using our 10 mK dilution refrigerator in collaboration with NIST-Boulder who supplied the qubit device.