| 1. |
- Kudra, Marina, 1992, et al.
(författare)
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Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences
- 2022
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Ingår i: PRX Quantum. - : AMER PHYSICAL SOC. - 2691-3399. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- Hosting nonclassical states of light in three-dimensional microwave cavities has emerged as a promising paradigm for continuous-variable quantum information processing. Here we experimentally demonstrate high-fidelity generation of a range of Wigner-negative states useful for quantum computation, such as Schrodinger-cat states, binomial states, Gottesman-Kitaev-Preskill states, as well as cubic phase states. The latter states have been long sought after in quantum optics and have never been achieved experimentally before. We use a sequence of interleaved selective number-dependent arbitrary phase (SNAP) gates and displacements. We optimize the state preparation in two steps. First we use a gradient-descent algorithm to optimize the parameters of the SNAP and displacement gates. Then we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly nonclassical states in a harmonic oscillator is robust to fluctuations of the system parameters such as the qubit frequency and the dispersive shift.
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| 2. |
- Ali, Aamir, 1994, et al.
(författare)
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Engineering Symmetry-Selective Couplings of a Superconducting Artificial Molecule to Microwave Waveguides
- 2022
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 129:12
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Tidskriftsartikel (refereegranskat)abstract
- Tailoring the decay rate of structured quantum emitters into their environment opens new avenues for nonlinear quantum optics, collective phenomena, and quantum communications. Here, we demonstrate a novel coupling scheme between an artificial molecule comprising two identical, strongly coupled transmon qubits and two microwave waveguides. In our scheme, the coupling is engineered so that transitions between states of the same (opposite) symmetry, with respect to the permutation operator, are predominantly coupled to one (the other) waveguide. The symmetry-based coupling selectivity, as quantified by the ratio of the coupling strengths, exceeds a factor of 30 for both waveguides in our device. In addition, we implement a Raman process activated by simultaneously driving both waveguides, and show that it can be used to coherently couple states of different symmetry in the single-excitation manifold of the molecule. Using that process, we implement frequency conversion across the waveguides, mediated by the molecule, with efficiency of about 95%. Finally, we show that this coupling arrangement makes it possible to straightforwardly generate spatially separated Bell states propagating across the waveguides. We envisage further applications to quantum thermodynamics, microwave photodetection, and photon-photon gates.
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| 3. |
- Jolin, Shan Williams, et al.
(författare)
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Multipartite Entanglement in a Microwave Frequency Comb
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 130:12
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Tidskriftsartikel (refereegranskat)abstract
- Significant progress has been made with multipartite entanglement of discrete qubits, but continuous variable systems may provide a more scalable path toward entanglement of large ensembles. We demonstrate multipartite entanglement in a microwave frequency comb generated by a Josephson parametric amplifier subject to a bichromatic pump. We find 64 correlated modes in the transmission line using a multifrequency digital signal processing platform. Full inseparability is verified in a subset of seven modes. Our method can be expanded to generate even more entangled modes in the near future.
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| 4. |
- Yang, Jiaying, 1995, et al.
(författare)
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Deterministic generation of shaped single microwave photons using a parametrically driven coupler
- 2023
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Ingår i: Physical Review Applied. - 2331-7019. ; 20:5
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Tidskriftsartikel (refereegranskat)abstract
- A distributed quantum computing system requires a quantum communication channel between spatially separated processing units. In superconducting circuits, such a channel can be realized by using propagating microwave photons to encode and transfer quantum information between an emitter and a receiver node. Here we experimentally demonstrate a superconducting circuit that deterministically transfers the state of a data qubit into a propagating microwave mode, with a process fidelity of 94.5%. We use a time-varying parametric drive to shape the temporal profile of the propagating mode to be time symmetric and with constant phase, so that reabsorption by the receiving processor can be implemented as a time-reversed version of the emission. We demonstrate a self-calibrating routine to correct for time-dependent shifts of the emitted frequencies due to the modulation of the parametric drive. Our work provides a reliable method to implement high-fidelity quantum state transfer and remote entanglement operations in a distributed quantum computing network.
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| 5. |
- Lu, Yong, 1989, et al.
(författare)
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Propagating Wigner-Negative States Generated from the Steady-State Emission of a Superconducting Qubit
- 2021
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 126:25
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate the steady-state generation of propagating Wigner-negative states from a continuously driven superconducting qubit. We reconstruct the Wigner function of the radiation emitted into propagating modes defined by their temporal envelopes, using digital filtering. For an optimized temporal filter, we observe a large Wigner logarithmic negativity, in excess of 0.08, in agreement with theory. The fidelity between the theoretical predictions and the states generated experimentally is up to 99%, reaching state-of-the-art realizations in the microwave frequency domain. Our results provide a new way to generate and control nonclassical states, and may enable promising applications such as quantum networks and quantum computation based on waveguide quantum electrodynamics.
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| 6. |
- Quijandria Diaz, Isaac Fernando, 1982, et al.
(författare)
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Steady-State Generation of Wigner-Negative States in One-Dimensional Resonance Fluorescence
- 2018
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 121:26
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Tidskriftsartikel (refereegranskat)abstract
- In this work we demonstrate numerically that the nonlinearity provided by a continuously driven two-level system allows for the generation of Wigner-negative states of the electromagnetic field confined in one spatial dimension. Wigner-negative states, also known as Wigner nonclassical states, are desirable for quantum information protocols beyond the scope of classical computers. Focusing on the steady-state emission from the two-level system, we find the largest negativity at the drive strength where the coherent reflection vanishes.
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| 7. |
- Strandberg, Emelie, et al.
(författare)
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Who makes it all the way? : Participants vs. decliners, and completers vs. drop-outs, in a 6-month exercise trial during cancer treatment. Results from the Phys-Can RCT
- 2022
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Ingår i: Supportive Care in Cancer. - : Springer Nature. - 0941-4355 .- 1433-7339. ; 30:2, s. 1739-1748
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To compare sociodemographic, health- and exercise-related characteristics of participants vs. decliners, and completers vs. drop-outs, in an exercise intervention trial during cancer treatment.Methods Patients with newly diagnosed breast, prostate, or colorectal cancer were invited to participate in a 6-month exercise intervention. Background data for all respondents (n = 2051) were collected at baseline by questionnaire and medical records. Additional data were collected using an extended questionnaire, physical activity monitors, and fitness testing for trial participants (n = 577). Moreover, a sub-group of decliners (n = 436) consented to additional data collection by an extended questionnaire . Data were analyzed for between-group differences using independent t-tests and chi2-tests.Results Trial participants were younger (59 ± 12yrs vs. 64 ± 11yrs, p < .001), more likely to be women (80% vs. 75%, p = .012), and scheduled for chemotherapy treatment (54% vs. 34%, p < .001), compared to decliners (n = 1391). A greater proportion had university education (60% vs 40%, p < .001), reported higher anxiety and fatigue, higher exercise self-efficacy and outcome expectations, and less kinesiophobia at baseline compared to decliners. A greater proportion of trial participants were classified as ‘not physically active’ at baseline; however, within the group who participated, being “physically active” at baseline was associated with trial completion. Completers (n = 410) also reported less kinesiophobia than drop-outs (n = 167).Conclusion The recruitment procedures used in comprehensive oncology exercise trials should specifically address barriers for participation among men, patients without university education and older patients. Individualized efforts should be made to enroll patients with low exercise self-efficacy and low outcome expectations of exercise. To retain participants in an ongoing exercise intervention, extra support may be needed for patients with kinesiophobia and those lacking health-enhancing exercise habits at baseline.
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| 8. |
- Strandberg, Ingrid, 1990
(författare)
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Generation and characterization of microwave quantum states
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum mechanics is the branch of physics that describes the properties and behavior of systems on the atomic and subatomic level. Over the past decades there has also been considerable progress in engineering larger-scale quantum systems. In this day and age, quantum information and quantum technology are rapidly developing areas of research where quantum effects are harnessed to improve sensitivity in measurements, encrypt secure communications, and enhance the performance of information processing and computing. Specific types of quantum states are needed for these purposes, and they can be challenging to generate in practice. This thesis describes methods to generate and characterize microwave states that could be useful for quantum computing protocols based on quantum states of light.
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| 9. |
- Strandberg, Ingrid, 1990, et al.
(författare)
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Numerical study of Wigner negativity in one-dimensional steady-state resonance fluorescence
- 2019
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 100:6
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Tidskriftsartikel (refereegranskat)abstract
- In a numerical study, we investigate the steady-state generation of nonclassical states of light from a coherently driven two-level atom in a one-dimensional waveguide. Specifically, we look for states with a negative Wigner function, since such nonclassical states are a resource for quantum information processing applications, including quantum computing. We find that a waveguide terminated by a mirror at the position of the atom can provide Wigner-negative states, while an infinite waveguide yields strictly positive Wigner functions. Moreover, our paper reveals a connection between the purity of a quantum state and its Wigner negativity. We also analyze the effects of decoherence on the negativity of a state.
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| 10. |
- Strandberg, Ingrid, 1990
(författare)
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Realistic prospect for continuous variable quantum computing in circuit-QED
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis is an extended introduction to the appended papers, which pertain to finding quantum states that are useful for continuous variable quantum computing. The useful states are characterized by a negative Wigner function. This is the underlying motivation for the appended papers, but why a negative Wigner function is necessary is not explained in the papers. This is elucidated in this thesis, with an accompanying discussion of which quantum mechanical properties allow quantum computers to surpass the capabilities of classical computers.
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