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Artificial atoms, realised in the form of supercon- ducting circuits, allow one to bypass the predeter- mined properties of naturally-occurring systems, and engage in the study of previously inaccessible quantum optics phenomena. The variability and scal- ability that artificial atoms can be made with, spell a bright future for these devices in metrological, quan- tum information processing and sensing fields. As part of an ongoing investigation, emissions re- sulting from relaxations in a Three-Level artificial atom were studied in this experiment. Demonstrated was the ability of the artificial atom to mediate intef- erence in applied microwave fields and produce con- trollable emission signals. The Thee-Level system will strongly interact with mi- crowave photons, whose frequencies correspond to the internal resonances in the system, . States and become coupled, as the system absorbs the resonant photons and undergoes a transition , from which it will susequently relax with rates . The photons are sent down a 1D transmission line in the form of a microwave field, and their energy is transferred to the artificial atom via the grid-like ca- pacitor. The amplitude of the microwave field deter- mines the Rabi frequency, , of the drive. The stronger the driving field, the larger the Rabi splitting, , of the coupled levels. A single resonant drive, cou- pling levels and , results in two coherent fields in the output line originating from: • The intial driving field • Photons emitted in ,,,,,,zzzzzzzzzrelaxations. The relative phase shift of between the two fields results in destructive interference, the prominence of which depends on the driving field Rabi fre- quency, , and detuning from the resonant ,,,,, transi- tion, , A special note of appreciation must be given to Dr. Shaikaidarov and Teresa Honigl De- crinis for their continous support over the course of the project, and Prof. Astafiev as the driving force behind the investigation. [1] Figure reproduced from Y. Qiu et. al, Sci Rep, vol. 6, pp. 28622, 2016. For any queries, please contact [email protected] Motivations for the project The flux artificial atom |j 〉 |i〉 ω ji Ω ji |i〉→|j 〉 Ω ji Γ jk ρ The stationary state of the system, , under an external drive is found from the Markovian master equation where is the Hamiltonian for the Three-Level atom and the driving field, and de- scribes incoherent relaxation processes in the system. Each time the system under- goes a relaxation , a photon of angular frequency , is emitted into the trans- mission line, where it pro- ceeds to travel in one of the two directions. The average field is in antiphase with the driving , ,,,,,,,,field(s), allowing the possibility of ,,,,,,,,,,,,intereference in the output line. ˙ ρ = - i [H,ρ]+ L[ρ] ≡ 0, H L[ρ] |j 〉→|i〉 ω ji |j 〉 |i〉 |j 〉→|i〉 〈V emitted 〉 = e iπ Γ ji 2 ρ ji π Ω ji |i〉→|j 〉 δω ji Re(t ji )=1 - Γ ji 2γ ji 1+ iδω ji /γ ji 1+(δω ji /γ ji ) 2 +Ω 2 ji /Γ ji γ ji t ji Γ ji ,γ ji Further features of interest are observed under two resonant driving fields. The Rabi splitting of the energy levels, that ensues upon strong drives, enriches the emission spectrum of the atom, by allowing off-resonance relaxation to take place. This is monitored by measuring the emission of the atom between the two undriven levels. The simulated emissions, eva- luted using dephasing pa- rameters found during interfer- ence observa- tions, qualita- tively agree with the meas- urements made on the driven system. The splitting fea- tures observed for stronge drives, are a direct con- squence of the Rabi splitting of the levels. Interacting with the system quantifies the ratio of the applied and outgoing signal. A least square fit to measured transmission values extracts the relaxation and decoherence rates of the system. Acknowledgements Relaxation phenomena in a Three-Level artificial atom Supervised by Prof. O. Astafiev Ilya Antonov Simulating response The artificial atom is a superconducting loop interrupted by four Josephson Junc- tions. The geometry of the junctions is chosen such that Josephson energies (dependent on phase) dominate over the charging energies (dependent on number of electrons), so that the atom operates on the flux degree of freedom. The applied flux selects the resonant transition frequencies, , , in the artifical atom. ω ji IN OUT IN 1.7 1.5 0.49 0.50 0.51 Φ/Φ 0 Working region |3〉 |2〉 |1〉 ω 32 ω 31 ω 21 1.8 1.6 1.4 Chosen working point on the energy spectrum of the arficial atom [1]. E/E J Mapping emissions from artifical atom relaxations • Capacitive coupling Destructive interference observation 1st Al Layer Aluminium Oxide 2nd Aluminium Layer • 13mK • Atom constrained to emit into 1D tranmission line ω 31 ω 21 Ω 31 Ω 21 Ω 21 Ω 21 Γ 21 Γ 32 Γ 31 Energy level structure for a strong drive, and a weak drive. |1〉→|2〉 |3〉 |2〉 |1〉 |1〉→|3〉 -80 -40 0 40 80 0.3 0.4 0.5 0.6 0.7 0.8 0.9 |2〉 |1〉 Ω 21 δω 21 Fing of transmission curves for the drive. |1〉→|2〉 -200 -150 -100 -50 0 50 100 150 20 -200 -150 -100 -50 0 50 100 150 200 -200 -150 -100 -50 0 50 100 150 -200 -150 -100 -50 0 50 100 150 200 -150 -100 -50 0 50 100 150 200 δω 31 /2π (MHz) δω 32 /2π (MHz) δω 21 /2π (MHz) Ω 32 = 210, Ω 31 = 20 MHz Ω 32 = 20, Ω 31 = 200 MHz Ω 21 = 50, Ω 31 = 60 MHz Ω 32 = 20, Ω 31 = 20 MHz 0 10 Emissions spectra for driving configuraons , , (top and boom leſt) and , (red). The ranges on the inset simulaons run from ± 200 MHz. |2〉→|3〉 |1〉→|2〉 |1〉→|3〉 |1〉→|3〉
