| 1. |
- Andersson, Gustav, 1990, et al.
(author)
-
Acoustic spectral hole-burning in a two-level system ensemble
- 2021
-
In: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 7:1
-
Journal article (peer-reviewed)abstract
- Microscopic two-level system (TLS) defects at dielectric surfaces and interfaces are among the dominant sources of loss in superconducting quantum circuits, and their properties have been extensively probed using superconducting resonators and qubits. We report on spectroscopy of TLSs coupling to the strain field in a surface acoustic wave (SAW) resonator. The narrow free spectral range of the resonator allows for two-tone spectroscopy where a strong pump is applied at one resonance, while a weak signal is used to probe a different mode. We map the spectral hole burnt by the pump tone as a function of frequency and extract parameters of the TLS ensemble. Our results suggest that detuned acoustic pumping can be used to enhance the coherence of superconducting devices by saturating TLSs.
|
|
| 2. |
- Andersson, Gustav, 1990, et al.
(author)
-
Electromagnetically Induced Acoustic Transparency with a Superconducting Circuit
- 2020
-
In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 124:24
-
Journal article (peer-reviewed)abstract
- We report the observation of electromagnetically induced transparency (EIT) of a mechanical field, where a superconducting artificial atom is coupled to a 1D-transmission line for surface acoustic waves. An electromagnetic microwave drive is used as the control field, rendering the superconducting transmon qubit transparent to the acoustic probe beam. The strong frequency dependence of the acoustic coupling enables EIT in a ladder configuration due to the suppressed relaxation of the upper level. Our results show that superconducting circuits can be engineered to interact with acoustic fields in parameter regimes not readily accessible to purely electromagnetic systems.
|
|
| 3. |
- Andersson, Gustav, 1990, et al.
(author)
-
Squeezing and Multimode Entanglement of Surface Acoustic Wave Phonons
- 2022
-
In: PRX Quantum. - 2691-3399. ; 3:1
-
Journal article (peer-reviewed)abstract
- Exploiting multiple modes in a quantum acoustic device could enable applications in quantum information in a hardware-efficient setup, including quantum simulation in a synthetic dimension and continuous-variable quantum computing with cluster states. We develop a multimode surface acoustic wave (SAW) resonator with a superconducting quantum interference device (SQUID) integrated in one of the Bragg reflectors. The interaction with the SQUID-shunted mirror gives rise to coupling between the more than 20 accessible resonator modes. We exploit this coupling to demonstrate two-mode squeezing of SAW phonons, as well as four-mode multipartite entanglement. Our results open avenues for continuous-variable quantum computing in a compact hybrid quantum system.
|
|
| 4. |
- Andersson, Gustav, et al.
(author)
-
Squeezing and Multimode Entanglement of Surface Acoustic Wave Phonons
- 2022
-
In: PRX Quantum. - : American Physical Society (APS). - 2691-3399. ; 3:1
-
Journal article (peer-reviewed)abstract
- Exploiting multiple modes in a quantum acoustic device could enable applications in quantum information in a hardware-efficient setup, including quantum simulation in a synthetic dimension and continuous-variable quantum computing with cluster states. We develop a multimode surface acoustic wave (SAW) resonator with a superconducting quantum interference device (SQUID) integrated in one of the Bragg reflectors. The interaction with the SQUID-shunted mirror gives rise to coupling between the more than 20 accessible resonator modes. We exploit this coupling to demonstrate two-mode squeezing of SAW phonons, as well as four-mode multipartite entanglement. Our results open avenues for continuous-variable quantum computing in a compact hybrid quantum system.
|
|
| 5. |
- Ankel, Martin, 1996, et al.
(author)
-
Bistatic noise radar: Demonstration of correlation noise suppression
- 2023
-
In: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8792 .- 1751-8784. ; 17:3, s. 351-361
-
Journal article (peer-reviewed)abstract
- In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudo-random noise, generated digitally at the receiver and transmitter units. Correlation losses, due to non-linearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.
|
|
| 6. |
- Ankel, Martin, 1996, et al.
(author)
-
Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
-
In: 20th European Radar Conference, EuRAD 2023. ; , s. 213-216
-
Conference paper (peer-reviewed)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
|
|
| 7. |
- Ankel, Martin, et al.
(author)
-
Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
-
In: Proceedings 20th European Radar Conference (EuRAD). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 213-216
-
Conference paper (peer-reviewed)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
|
|
| 8. |
- Ankel, Martin, 1996, et al.
(author)
-
Implementation of a coherent real‐time noise radar system
- 2023
-
In: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792.
-
Journal article (peer-reviewed)abstract
- The utilisation of continuous random waveforms for radar, that is, noise radar, has been extensively studied as a candidate for low probability of intercept operation. However, compared with the more traditional pulse-Doppler radar, noise radar systems are significantly more complicated to implement, which is likely why few systems exist. If noise radar systems are to see the light of day, system design, implementation, limitations etc., must be investigated. Therefore, the authors examine and detail the implementation of a real-time noise radar system on a field programmable gate array. The system is capable of operating with 100% duty cycle, 200 MHz bandwidth, and 268 ms integration time while processing a range of about 8.5 km. Additionally, the system can perform real-time moving target compensation to reduce cell migration. System performance is primarily limited by the memory bandwidth of the off-chip dynamic random access memory.
|
|
| 9. |
- Bengtsson, Andreas, 1991, et al.
(author)
-
Improved Success Probability with Greater Circuit Depth for the Quantum Approximate Optimization Algorithm
- 2020
-
In: Physical Review Applied. - 2331-7019. ; 14:3
-
Journal article (peer-reviewed)abstract
- Present-day, noisy, small or intermediate-scale quantum processors-although far from fault tolerant-support the execution of heuristic quantum algorithms, which might enable a quantum advantage, for example, when applied to combinatorial optimization problems. On small-scale quantum processors, validations of such algorithms serve as important technology demonstrators. We implement the quantum approximate optimization algorithm on our hardware platform, consisting of two superconducting transmon qubits and one parametrically modulated coupler. We solve small instances of the NP (nondeterministic polynomial time)-complete exact-cover problem, with 96.6% success probability, by iterating the algorithm up to level two.
|
|
| 10. |
- Chen, Liangyu, 1994, et al.
(author)
-
Transmon qubit readout fidelity at the threshold for quantum error correction without a quantum-limited amplifier
- 2023
-
In: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 9:1
-
Journal article (peer-reviewed)abstract
- High-fidelity and rapid readout of a qubit state is key to quantum computing and communication, and it is a prerequisite for quantum error correction. We present a readout scheme for superconducting qubits that combines two microwave techniques: applying a shelving technique to the qubit that reduces the contribution of decay error during readout, and a two-tone excitation of the readout resonator to distinguish among qubit populations in higher energy levels. Using a machine-learning algorithm to post-process the two-tone measurement results further improves the qubit-state assignment fidelity. We perform single-shot frequency-multiplexed qubit readout, with a 140 ns readout time, and demonstrate 99.5% assignment fidelity for two-state readout and 96.9% for three-state readout–without using a quantum-limited amplifier.
|
|
