| 1. |
- Lu, Yong, 1989, et al.
(författare)
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Characterizing decoherence rates of a superconducting qubit by direct microwave scattering
- 2021
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally investigate a superconducting qubit coupled to the end of an open transmission line, in a regime where the qubit decay rates to the transmission line and to its own environment are comparable. We perform measurements of coherent and incoherent scattering, on- and off-resonant fluorescence, and time-resolved dynamics to determine the decay and decoherence rates of the qubit. In particular, these measurements let us discriminate between non-radiative decay and pure dephasing. We combine and contrast results across all methods and find consistent values for the extracted rates. The results show that the pure dephasing rate is one order of magnitude smaller than the non-radiative decay rate for our qubit. Our results indicate a pathway to benchmark decoherence rates of superconducting qubits in a resonator-free setting.
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| 2. |
- Lu, Yong, 1989, et al.
(författare)
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Quantum efficiency, purity and stability of a tunable, narrowband microwave single-photon source
- 2021
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.
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| 3. |
- Andersson, Gustav, 1990, et al.
(författare)
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Non-exponential decay of a giant artificial atom
- 2019
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 15:11, s. 1123-1127
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In quantum optics, light–matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions1,2. In contrast, here we experimentally demonstrate the vastly different ‘giant atom’ regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit3 to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics4. We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as non-exponential relaxation in the time domain.
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| 4. |
- Ekström, Maria, 1988, et al.
(författare)
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Towards phonon routing: controlling propagating acoustic waves in the quantum regime
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- We explore routing of propagating phonons in analogy with previous experiments on photons. Surface acoustic waves (SAWs) in the microwave regime are scattered by a superconducting transmon qubit. The transmon can be tuned on or off resonance with the incident SAW field using an external magnetic field or the Autler-Townes effect, and thus the reflection and transmission of the SAW field can be controlled in time. We observe 80% extinction in the transmission of the low power continuous signal and a 40 ns rise time of the router. The slow propagation speed of SAWs on solid surfaces allows for in-flight manipulations of the propagating phonons. The ability to route short, 100 ns, pulses enables new functionality, for instance to catch an acoustic phonon between two qubits and then release it in a controlled direction.
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| 5. |
- Novikov, S., et al.
(författare)
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Raman coherence in a circuit quantum electrodynamics lambda system
- 2016
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 12:1, s. 75-79
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Tidskriftsartikel (refereegranskat)abstract
- Atomic three-level systems dressed by two coherent electromagnetic fields can exhibit coherent population trapping and electromagnetically induced transparency (EIT) due to quantum interference. By addressing the combined qubit-cavity states of a superconducting transmon qubit in a three-dimensional copper cavity with two microwave drives we establish an effective system, two legs of which are defined by a dipole transition and a two-photon transition. This circuit-based system allows the observation of three-microwave-photon Raman coherence effects, including coherent population trapping and EIT, which are demonstrated here with both steady-state spectroscopic techniques and time-domain measurements. By sending Gaussian microwave pulses through the cavity in the EIT regime, a negative group velocity of the pulse is observed with the peak of the pulse exiting the cavity 9.4 μs before entering.
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| 6. |
- Suri, Baladitya, 1984, et al.
(författare)
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Nonlinear microwave photon occupancy of a driven resonator strongly coupled to a transmon qubit
- 2015
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 92:6
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Tidskriftsartikel (refereegranskat)abstract
- We measure photon occupancy in a thin-film superconducting lumped element resonator coupled to a transmon qubit at 20mK and find a nonlinear dependence on the applied microwave power. The transmon-resonator system was operated in the strong dispersive regime, where the ac Stark shift (2χ) due to a single microwave photon present in the resonator was larger than the linewidth (Γ) of the qubit transition. When the resonator was coherently driven at 5.474 325 GHz, the transition spectrum of the transmon at 4.982 GHz revealed well-resolved peaks, each corresponding to an individual photon number-state of the resonator. From the relative peak heights we obtain the occupancy of the photon states and the average photon occupancy n¯ of the resonator. We observe a nonlinear variation of n¯ with the applied drive power Prf for n¯
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