Low-loss waveguides are required for quantum communication at distances beyond the chip-scale for any low-temperature solid-state implementation of quantum information processors. We measure and analyze the attenuation constant of commercially available microwave-frequency waveguides down to millikelvin temperatures and single photon levels. More specifically, we characterize the frequency-dependent loss of a range of coaxial and rectangular microwave waveguides down to $0.005\ \mbox{dB}/\mbox{m}$ using a resonant-cavity technique. We study the loss tangent and relative permittivity of commonly used dielectric waveguide materials by measurements of the internal quality factors and their comparison with established loss models. The results of our characterization are relevant for accurately predicting the signal levels at the input of cryogenic devices, for reducing the loss in any detection chain, and for estimating the heat load induced by signal dissipation in cryogenic systems.Low-loss waveguides are required for quantum communication at distances beyond the chip-scale for any low-temperature solid-state implementation of quantum information processors. We measure and analyze the attenuation constant of commercially available microwave-frequency waveguides down to millikelvin temperatures and single photon levels. More specifically, we characterize the frequency-dependent loss of a range of coaxial and rectangular microwave waveguides down to $0.005\ \mbox{dB}/\mbox{m}$ using a resonant-cavity technique. We study the loss tangent and relative permittivity of commonly used dielectric waveguide materials by measurements of the internal quality factors and their comparison with established loss models. The results of our characterization are relevant for accurately predicting the signal levels at the input of cryogenic devices, for reducing the loss in any detection chain, and for estimating the heat load induced by signal dissipation in cryogenic systems.

arXiv:1612.07977EPJ Quantum TechnologyMay 4, 201744 citations

Quantum state characterization of a fast tunable superconducting resonator

Z. L. Wang, Youpeng Zhong, L. J. He +4 more

We demonstrate a frequency-tunable superconducting coplanar waveguide resonator, with a tuning range of half a gigahertz and a switching time of 1 ns. The resonator is made tunable by inserting a superconducting quantum interference device in the center strip of the resonator. Quantum measurements are made by probing the resonator with a superconducting qubit, allowing us to use microwave photon Fock states to benchmark the resonator performance. Using the resonator, we shuttle energy quanta between the qubit and a microscopic two-level state. The tunable resonator can, therefore, serve as a communication bus or memory element in a prototype quantum processor.We demonstrate a frequency-tunable superconducting coplanar waveguide resonator, with a tuning range of half a gigahertz and a switching time of 1 ns. The resonator is made tunable by inserting a superconducting quantum interference device in the center strip of the resonator. Quantum measurements are made by probing the resonator with a superconducting qubit, allowing us to use microwave photon Fock states to benchmark the resonator performance. Using the resonator, we shuttle energy quanta between the qubit and a microscopic two-level state. The tunable resonator can, therefore, serve as a communication bus or memory element in a prototype quantum processor.

Applied Physics LettersApr 22, 201374 citations

Quantum Communication with Microwave Photons

Andreas J. Wallraff

Bulletin of the American Physical SocietyMar 4, 20190 citations

Quantum Optics at Microwave Frequencies

Daniel F. Walls, Gerard J Milburn

Graduate texts in physicsJan 1, 20250 citations

Characterizing Niobium Nitride-Based Superconducting Coplanar Waveguide Resonators for Microwave Hybrid Circuit Quantum Electrodynamics

Paniz Foshat, Paul Baity, Sergey Danilin +8 more

The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material for applications in superconducting quantum technology. However, NbN-based superconducting circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor ( $Q_{i}$ ) decreases from $Q_{i}\sim 1.07\times 10^{6}$ in a high power regime to $Q_{i}\sim 1.36\times 10^{5}$ in the single photon regime. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature ( $T$ ) dependence of $Q_{i}$ and resonance frequency $f_{r}$ of coplanar waveguide resonators to characterize the quasiparticle density. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure $f_{r}$ and $Q_{i}$ in response to in-plane magnetic fields ( $B_{||}$ ). We verify that $Q_{i}$ stays well above $10^{4}$ up to $B_{||}$ = 240 mT in the photon number $< \! n_{ph} \! >$ = 1.8 at $T$ = 100 mK. Our results could enable the development of robust microwave superconducting circuits for circuit quantum electrodynamics at high magnetic fields required for hybrid superconducting-semiconducting quantum circuits.The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material for applications in superconducting quantum technology. However, NbN-based superconducting circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor ($Q_{i}$) decreases from$Q_{i}\sim 1.07\times 10^{6}$in a high power regime to$Q_{i}\sim 1.36\times 10^{5}$in the single photon regime. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature ($T$) dependence of$Q_{i}$and resonance frequency$f_{r}$of coplanar waveguide resonators to characterize the quasiparticle density. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure$f_{r}$and$Q_{i}$in response to in-plane magnetic fields ($B_{||}$). We verify that$Q_{i}$stays well above$10^{4}$up to$B_{||}$= 240 mT in the photon number$< \! n_{ph} \! >$= 1.8 at$T$= 100 mK. Our results could enable the development of robust microwave superconducting circuits for circuit quantum electrodynamics at high magnetic fields required for hybrid superconducting-semiconducting quantum circuits.

IEEE Transactions on Applied SuperconductivityJan 22, 202510 citations

Q_{i}

) decreases from

Q_{i}\sim 1.07\times 10^{6}

in a high power regime to

Q_{i}\sim 1.36\times 10^{5}

in the single photon regime. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature (

T

) dependence of

Q_{i}

and resonance frequency

f_{r}

of coplanar waveguide resonators to characterize the quasiparticle density. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure

f_{r}

and

Q_{i}

in response to in-plane magnetic fields (

B_{||}

). We verify that

Q_{i}

stays well above

10^{4}

up to

B_{||}

= 240 mT in the photon number

< \! n_{ph} \! >

= 1.8 at

T

= 100 mK. Our results could enable the development of robust microwave superconducting circuits for circuit quantum electrodynamics at high magnetic fields required for hybrid superconducting-semiconducting quantum circuits.