| 1. |
- Gambetta, Filippo M., et al.
(författare)
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Exploring the Many-Body Dynamics Near a Conical Intersection with Trapped Rydberg Ions
- 2021
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 126:23
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Tidskriftsartikel (refereegranskat)abstract
- Conical intersections between electronic potential energy surfaces are paradigmatic for the study of nonadiabatic processes in the excited states of large molecules. However, since the corresponding dynamics occurs on a femtosecond timescale, their investigation remains challenging and requires ultrafast spectroscopy techniques. We demonstrate that trapped Rydberg ions are a platform to engineer conical intersections and to simulate their ensuing dynamics on larger length scales and timescales of the order of nanometers and microseconds, respectively; all this in a highly controllable system. Here, the shape of the potential energy surfaces and the position of the conical intersection can be tuned thanks to the interplay between the high polarizability and the strong dipolar exchange interactions of Rydberg ions. We study how the presence of a conical intersection affects both the nuclear and electronic dynamics demonstrating, in particular, how it results in the inhibition of the nuclear motion. These effects can be monitored in real time via a direct spectroscopic measurement of the electronic populations in a state-of-the-art experimental setup.
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| 2. |
- Gambetta, Filippo M., et al.
(författare)
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Long-range multi-body interactions and three-body anti-blockade in a trapped Rydberg ion chain
- 2020
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 125:13
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Tidskriftsartikel (refereegranskat)abstract
- Trapped Rydberg ions represent a flexible platform for quantum simulation and information processing which combines a high degree of control over electronic and vibrational degrees of freedom. The possibility to individually excite ions to high-lying Rydberg levels provides a system where strong and long-range interactions between pairs of excited ions can be engineered and tuned via external laser fields. We show that the coupling between Rydberg pair interactions and collective motional modes gives rise to effective long-range multi-body interactions, consisting of two, three, and four-body terms. Their shape, strength, and range can be controlled via the ion trap parameters and strongly depends on both the equilibrium configuration and vibrational modes of the ion crystal. By focusing on an experimentally feasible quasi one-dimensional setup of 88Sr+ Rydberg ions, we demonstrate that multi-body interactions are enhanced by the emergence of a soft mode associated, e.g., with a structural phase transition. This has a striking impact on many-body electronic states and results, for example, in a three-body anti-blockade effect. Our study shows that trapped Rydberg ions offer new opportunities to study exotic many-body quantum dynamics driven by enhanced multi-body interactions.
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| 3. |
- Higgins, Gerard, 1989-
(författare)
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A single trapped Rydberg ion
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Systems of trapped ions and systems of ultracold Rydberg atoms are used at the forefront of quantum physics research and they make strong contenders as platforms for quantum technologies. Trapped Rydberg ions are a new hybrid technology envisaged to have both the exquisite control of trapped ion systems and the strong interactions of Rydberg atoms. In this work a single trapped Rydberg ion is experimentally investigated. A trapped 88Sr+ ion is excited to Rydberg states using two ultraviolet lasers. Effects of the strong trapping electric fields on the sensitive Rydberg ion are studied. After mitigating unwanted trap effects, the ion is coherently excited to Rydberg states and a quantum gate is demonstrated. This thesis lays much of the experimental groundwork for research using this novel system.
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| 4. |
- Higgins, Gerard, et al.
(författare)
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Coherent Control of a Single Trapped Rydberg Ion
- 2017
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:22
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Tidskriftsartikel (refereegranskat)abstract
- Trapped Rydberg ions are a promising novel approach to quantum computing and simulations. They are envisaged to combine the exquisite control of trapped ion qubits with the fast two-qubit Rydberg gates already demonstrated in neutral atom experiments. Coherent Rydberg excitation is a key requirement for these gates. Here, we carry out the first coherent Rydberg excitation of an ion and perform a single-qubit Rydberg gate, thus demonstrating basic elements of a trapped Rydberg ion quantum computer.
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| 5. |
- Higgins, Gerard, et al.
(författare)
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Highly Polarizable Rydberg Ion in a Paul Trap
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 123:15
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Tidskriftsartikel (refereegranskat)abstract
- Usually the influence of the quadratic Stark effect on an ion's trapping potential is minuscule and only needs to be considered in atomic clock experiments. In this work we excite a trapped ion to a Rydberg state with polarizability similar to 8 orders of magnitude higher than a low-lying electronic state; we find that the highly polarizable ion experiences a vastly different trapping potential owing to the Stark effect. We observe changes in trap stiffness, equilibrium position, and minimum potential, which can be tuned using the trapping electric fields. These effects lie at the heart of several proposed studies, including a high-fidelity submicrosecond entangling operation; in addition we demonstrate these effects may be used to minimize ion micromotion. Mitigation of Stark effects is important for coherent control of Rydberg ions; we illustrate this by carrying out the first Rabi oscillations between a low-lying electronic state and a Rydberg state of an ion.
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| 6. |
- Higgins, Gerard, 1989, et al.
(författare)
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Micromotion minimization using Ramsey interferometry
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:12
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Tidskriftsartikel (refereegranskat)abstract
- We minimize the stray electric field in a linear Paul trap quickly and accurately, by applying interferometry pulse sequences to a trapped ion optical qubit. The interferometry sequences are sensitive to the change of ion equilibrium position when the trap stiffness is changed, and we use this to determine the stray electric field. The simplest pulse sequence is a two-pulse Ramsey sequence, and longer sequences with multiple pulses offer a higher precision. The methods allow the stray field strength to be minimized beyond state-of-the-art levels. Using a sequence of nine pulses we reduce the 2D stray field strength to (10.5 +/- 0.8) mV m(-1) in 11 s measurement time. The pulse sequences are easy to implement and automate, and they are robust against laser detuning and pulse area errors. We use interferometry sequences with different lengths and precisions to measure the stray field with an uncertainty below the standard quantum limit. This marks a real-world case in which quantum metrology offers a significant enhancement. Also, we minimize micromotion in 2D using a single probe laser, by using an interferometry method together with the resolved sideband method; this is useful for experiments with restricted optical access. Furthermore, a technique presented in this work is related to quantum protocols for synchronizing clocks; we demonstrate these protocols here.
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| 7. |
- Higgins, Gerard, et al.
(författare)
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Observation of second- and higher-order electric quadrupole interactions with an atomic ion
- 2021
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Ingår i: Physical Review Research. - 2643-1564. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- The response of matter to fields underlies the physical sciences, from particle physics to astrophysics, and from chemistry to biophysics. We observe an atom's response to an electric quadrupole field to second- and higher orders; this arises from the atom's electric quadrupole polarizability and hyperpolarizabilities. We probe a single atomic ion which is excited to Rydberg states and confined in the electric fields of a Paul trap. The quadrupolar trapping fields cause atomic energy level shifts and give rise to spectral sidebands. The observed effects are described well by theory calculations.
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| 8. |
- Higgins, Gerard, et al.
(författare)
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Single Strontium Rydberg Ion Confined in a Paul Trap
- 2017
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Ingår i: Physical Review X. - 2160-3308. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- Trapped Rydberg ions are a promising new system for quantum information processing. They have the potential to join the precise quantum operations of trapped ions and the strong, long-range interactions between Rydberg atoms. Combining the two systems is not at all straightforward. Rydberg atoms are severely affected by electric fields which may cause Stark shifts and field ionization, while electric fields are used to trap ions. Thus, a thorough understanding of the physical properties of Rydberg ions due to the trapping electric fields is essential for future applications. Here, we report the observation of two fundamental trap effects. First, we investigate the interaction of the Rydberg electron with the trapping electric quadrupole fields which leads to Floquet sidebands in the excitation spectra. Second, we report on the modified trapping potential in the Rydberg state compared to the ground state that results from the strong polarizability of the Rydberg ion. By controlling both effects we observe resonance lines close to their natural linewidth demonstrating an unprecedented level of control of this novel quantum platform.
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| 9. |
- Lourenço, José A. S., et al.
(författare)
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Non-Hermitian dynamics and PT-symmetry breaking in interacting mesoscopic Rydberg platforms
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 106:2
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Tidskriftsartikel (refereegranskat)abstract
- We simulate the dissipative dynamics of a mesoscopic system of long-range interacting particles which can be mapped into non-Hermitian spin models with a PT symmetry. We find rich PT phase diagrams with PT-symmetric and PT-broken phases. The dynamical regimes can be further enriched by modulating tunable parameters of the system. We outline how the PT symmetries of such systems may be probed by studying their dynamics. We note that systems of Rydberg atoms and systems of Rydberg ions with strong dipolar interactions are particularly well suited for such studies. We present a viable proposal for implementing non-Hermitian physics with PT symmetry in Rydberg systems. We show that for realistic parameters, long-range interactions allow the emergence of new PT-symmetric regions, generating new PT phase transitions. In addition, such PT-symmetry phase transitions are found by changing the configurations of the Rydberg atoms. We propose a post selection scheme on an ensemble of Rydberg ions described by an effective three-level system. Detecting the population dynamics, the system shows an oscillatory behavior in the PT-unbroken phase and a stationary population for long times in the PT-broken phase.
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| 10. |
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| 11. |
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| 12. |
- Mallweger, Marion, et al.
(författare)
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Single-Shot Measurements of Phonon Number States Using the Autler-Townes Effect
- 2023
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 131:22
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Tidskriftsartikel (refereegranskat)abstract
- We present a single-shot method to measure motional states in the number basis. The technique can be applied to systems with at least three nondegenerate energy levels which can be coupled to a linear quantum harmonic oscillator. The method relies on probing an Autler-Townes splitting that arises when a phonon-number changing transition is strongly coupled. We demonstrate the method using a single trapped ion and show that it may be used in a nondemolition fashion to prepare phonon number states. We also show how the Autler-Townes splitting can be used to measure phonon number distributions.
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| 13. |
- Mallweger, Marion, 1997-, et al.
(författare)
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Single-Shot Measurements of Phonon Number States Using the Autler-Townes Effect
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:22
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Tidskriftsartikel (refereegranskat)abstract
- We present a single-shot method to measure motional states in the number basis. The technique can be applied to systems with at least three nondegenerate energy levels which can be coupled to a linear quantum harmonic oscillator. The method relies on probing an Autler-Townes splitting that arises when a phonon-number changing transition is strongly coupled. We demonstrate the method using a single trapped ion and show that it may be used in a nondemolition fashion to prepare phonon number states. We also show how the Autler-Townes splitting can be used to measure phonon number distributions.
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| 14. |
- Mokhberi, Arezoo, et al.
(författare)
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Trapped Rydberg ions : A new platform for quantum information processing
- 2020. - 1
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Ingår i: Advances In Atomic, Molecular, and Optical Physics. - Cambridge : Academic Press. - 9780128209875 ; , s. 233-306
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Bokkapitel (refereegranskat)abstract
- In this chapter, we present an overview of experiments with trapped Rydberg ions and outline the advantages and challenges of developing applications of this new platform for quantum computing, sensing, and simulation. Trapped Rydberg ions feature several important properties, unique in their combination: they are tightly bound in a harmonic potential of a Paul trap, in which their internal and external degrees of freedom can be controlled in a precise fashion. High fidelity state preparation of both internal and motional states of the ions has been demonstrated, and the internal states have been employed to store and manipulate qubit information. Furthermore, strong dipolar interactions can be realized between ions in Rydberg states and be explored for investigating correlated many body systems. By laser coupling to Rydberg states, the polarizability of the ions can be both enhanced and tuned. This can be used to control the interactions with the trapping fields in a Paul trap as well as dipolar interactions between the ions. Thus, trapped Rydberg ions present an attractive alternative for fast entangling operations as compared to those mediated by normal modes of trapped ions, which are advantageous for a future quantum computer or a quantum simulator.
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| 15. |
- Oliveira, Murilo H., et al.
(författare)
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Steady-state entanglement generation for nondegenerate qubits
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 107:2
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Tidskriftsartikel (refereegranskat)abstract
- We propose a scheme to dissipatively produce steady-state entanglement in a two-qubit system, via an interaction with a bosonic mode. The system is driven into a stationary entangled state, while we compensate the mode dissipation by injecting energy via a coherent pump field. We also present a scheme which allows us to adiabatically transfer all the population to the desired entangled state. The dynamics leading to the entangled state in these schemes can be understood in analogy with electromagnetically induced transparency and stimulated Raman adiabatic passage, respectively.
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| 16. |
- Parke, Harry
(författare)
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Applications of motional control in trapped Rydberg ion experiments
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trapped ion systems are one of the leading technologies for the development of various novel quantum devices, including computers, simulators and enhanced sensors. Ion traps offer a high level of control in terms of both the electronic and motional states of individual quantum systems. This enables information to be efficiently encoded and transferred, often via interaction with highly controlled laser fields. In particular, the use of collective motional excitation to generate entanglement is a principle that underlies the majority of gate operations that have thus far been implemented in trapped ion systems. Another method, originally devised to circumvent the need for collective motional excitation in entangling operations, is to use Rydberg states which can be engineered to produce strong, direct and state-dependent interactions between ions. Due to their sensitivity to electric fields, trapped Rydberg ions have also opened the possibility for the development of entirely new gate schemes and for use in quantum metrology. In this work we employ the high level of motional control available to trapped ion systems in order to perform three experiments, involving quantum simulation, computation and metrology respectively. In the first we make use of a single ion and couple its electronic and motional states to simulate sub- and superradiant emission for an atom confined in a 2D cavity. The results obtained showed that technical limitations in our experimental system currently inhibit the formation of such states. In the second experiment we introduce a novel gate scheme for quantum computation using trapped Rydberg ions, initial results demonstrating the feasibility of the gate scheme are presented and future plans for this work are summarised. For the final experiment we investigate the effects of an electric quadrupole field interacting with a single ion to second and higher orders. We observe resonance shifts for the Rydberg excitation and the presence of sidebands due to the interaction when performing spectral scans. These observations show good agreement when compared with theoretical models. Finally a new technique for performing coherent spectroscopy of Ryberg states is demonstrated.
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| 17. |
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| 18. |
- Pokorny, Fabian, 1988-
(författare)
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A microwave dressed Rydberg ion
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trapped Rydberg ions are a promising new platform for quantum computation and simulation. They combine the exquisite control of trapped ion systems with the strong dipole-dipole interactions available in Rydberg atom systems. In order to realize strong interactions between Rydberg ions, microwave dressing is required to induce strong oscillating dipoles. Additionally, microwave dressing of Rydberg states with polarizabilities of opposite sign allows for the realization of Rydberg states with vanishing polarizability. Such states are insensitive to external electric fields and can be trapped independently of their state. Vanishing-polarizability Rydberg states allow for implementing Rydberg entangling gates in large ion crystals.
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| 19. |
- Pokorny, Fabian, et al.
(författare)
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Magic trapping of a Rydberg ion with a diminished static polarizability
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Highly excited Rydberg states are usually extremely polarizable and exceedingly sensitive to electric fields. Because of this Rydberg ions confined in electric fields have state-dependent trapping potentials. We engineer a Rydberg state that is insensitive to electric fields by coupling two Rydberg states with static polarizabilities of opposite sign, in this way we achieve state-independent magic trapping. We show that the magically-trapped ion can be coherently excited to the Rydberg state without the need for control of the ion's motion.
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| 20. |
- Pokorny, Fabian, et al.
(författare)
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Tracking the Dynamics of an Ideal Quantum Measurement
- 2020
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 124:8
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Tidskriftsartikel (refereegranskat)abstract
- The existence of ideal quantum measurements is one of the fundamental predictions of quantum mechanics. In theory, an ideal measurement projects a quantum state onto the eigenbasis of the measurement observable, while preserving coherences between eigenstates that have the same eigenvalue. The question arises whether there are processes in nature that correspond to such ideal quantum measurements and how such processes are dynamically implemented in nature. Here we address this question and present experimental results monitoring the dynamics of a naturally occurring measurement process: the coupling of a trapped ion qutrit to the photon environment. By taking tomographic snapshots during the detection process, we show that the process develops in agreement with the model of an ideal quantum measurement with an average fidelity of 94%.
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| 21. |
- Thomm, Robin, 1994-
(författare)
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Towards quantum simulation and computing with trapped Rydberg ions
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trapped ions are widely used in quantum simulation, precision spectroscopy, quantum information and computation experiments. The excellent level of control, long coherence times and accessibility to commercially available instruments make them very attractive for these kind of experiments. Furthermore, the combination of external motional and internal electronic degrees of freedom can lead to rich and interesting dynamics. Here we present a novel technique to measure the motional state of the ion based on the Autler-Townes effect that is more efficient than the standard approach and can be employed in a non demolition manner. Furthermore, we use the combination of motional and electronic dynamics to simulate the dynamics of an atom in a cross cavity setup and investigate the emergence of interference both for quantum and coherent states. Both experiments are main results in other PhD theses and already published with major contributions from me. Moreover, the experimental setup was upgraded to allow for better motional control of the ion, better automatization with an up to date control system and an improved Rydberg addressing setup. Especially the last point will be crucial for future experiments since it allows controlled Rydberg excitation of individual ions in an ion string which will be needed for future research in quantum simulation and computation experiments with Rydberg ions.
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| 22. |
- Zhang, Chi, 1990-
(författare)
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Fast and Scalable Entangling Gate in Trapped Ions via Rydberg Interaction
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trapped Rydberg ions are a novel platform for quantum information processing. This approach combines the advanced quantum control of trapped ions and the strong dipolar interaction of Rydberg atoms. In this thesis, a strong dipole-dipole interaction has been demonstrated and a sub-microsecond entangling gate has been implemented in a cold two-ion crystal. After minimizing the polarizability of the Rydberg state by microwave dressing and understanding the effect of the quadrupole radio-frequency trap,the entangling gate has been applied in a warm 12-ion crystal.
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| 23. |
- Zhang, Chi, et al.
(författare)
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Submicrosecond entangling gate between trapped ions via Rydberg interaction
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 580:7803, s. 345-349
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Tidskriftsartikel (refereegranskat)abstract
- Generating quantum entanglement in large systems on timescales much shorter than the coherence time is key to powerful quantum simulation and computation. Trapped ions are among the most accurately controlled and best isolated quantum systems(1) with low-error entanglement gates operated within tens of microseconds using the vibrational motion of few-ion crystals(2,3). To exceed the level of complexity tractable by classical computers the main challenge is to realize fast entanglement operations in crystals made up of many ions (large ion crystals)(4). The strong dipole-dipole interactions in polar molecule(5) and Rydberg atom(6,7) systems allow much faster entangling gates, yet stable state-independent confinement comparable with trapped ions needs to be demonstrated in these systems(8). Here we combine the benefits of these approaches: we report a two-ion entangling gate with 700-nanosecond gate time that uses the strong dipolar interaction between trapped Rydberg ions, which we use to produce a Bell state with 78 per cent fidelity. The sources of gate error are identified and a total error of less than 0.2 per cent is predicted for experimentally achievable parameters. Furthermore, we predict that residual coupling to motional modes contributes an approximate gate error of 10(-4) in a large ion crystal of 100 ions. This provides a way to speed up and scale up trapped-ion quantum computers and simulators substantially.
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