High-Purity Entanglement of Hot Propagating Modes Using Nonreciprocity

Distributed quantum information processing and communication protocols demand the ability to generate entanglement among propagating modes. However, thermal fluctuations can severely limit the fidelity and purity of propagating entangled states, especially for low-frequency modes relevant for radio-frequency (rf) signals. Here, we propose nonreciprocity as a resource to render continuous-variable entanglement of propagating modes robust against thermal fluctuations. By utilizing a cold-engineered reservoir, we break the symmetry of reciprocity in a standard two-mode squeezing interaction between a low- and a high-frequency mode and show that the rerouting of thermal fluctuations allows the generation of flying entangled states with high purity. Our approach requires only pairwise Gaussian interactions and is thus ideal for parametric circuit-QED implementations

Nonuniversality of quantum noise in optical amplifiers operating at exceptional points

The concept of exceptional points-based optical amplifiers (EPOAs) has been recently proposed as a new paradigm for miniaturizing optical amplifiers while simultaneously enhancing their gain-bandwidth product. While the operation of this new family of amplifiers in the classical domain provides a clear advantage, their performance in the quantum domain has not yet been evaluated. Particularly, it is not clear how the quantum noise introduced by vacuum fluctuations will affect their operation. Here, we investigate this problem by considering three archetypal EPOA structures that rely either on unidirectional coupling, parity-time symmetry, or particle-hole symmetry for implementing the exceptional point. By using the Heisenberg-Langevin formalism, we calculate the added quantum noise in each of these devices and compare it with that of a quantum-limited amplifier scheme that does not involve any exceptional points. Our analysis reveals several interesting results: most notably that while the quantum noise of certain EPOAs can be comparable to those associated with conventional amplifier systems, in general the noise does not follow a universal scaling as a function of the exceptional point but rather varies from one implementation to another

Generalized nonreciprocity in an optomechanical circuit via synthetic magnetism and reservoir engineering

Synthetic magnetism has been used to control charge neutral excitations for applications ranging from classical beam steering to quantum simulation. In optomechanics, radiation-pressure-induced parametric coupling between optical (photon) and mechanical (phonon) excitations may be used to break time-reversal symmetry, providing the prerequisite for synthetic magnetism. Here we design and fabricate a silicon optomechanical circuit with both optical and mechanical connectivity between two optomechanical cavities. Driving the two cavities with phase-correlated laser light results in a synthetic magnetic flux, which in combination with dissipative coupling to the mechanical bath, leads to nonreciprocal transport of photons with 35dB of isolation. Additionally, optical pumping with blue-detuned light manifests as a particle non-conserving interaction between photons and phonons, resulting in directional optical amplification of 12dB in the isolator through direction. These results indicate the feasibility of utilizing optomechanical circuits to create a more general class of nonreciprocal optical devices, and further, to enable novel topological phases for both light and sound on a microchip.Comment: 18 pages, 8 figures, 4 appendice

Generation of large amplitude phonon states in quantum acoustics

The development of quantum acoustics has enabled the cooling of mechanical objects to their quantum ground state, generation of mechanical Fock-states, and Schrödinger cat states. Such demonstrations have made mechanical resonators attractive candidates for quantum information processing, metrology, and macroscopic tests of quantum mechanics. However, generating large-amplitude phonon states in quantum acoustic systems has been elusive. In this work, a single superconducting qubit coupled to a high-overtone bulk acoustic resonator is used to generate a large phonon population in an acoustic mode of a high-overtone resonator. We observe extended ringdowns of the qubit, confirming the generation of a large amplitude phonon state, and also observe an upper threshold behavior, a consequence of phonon quenching predicted by our model. This work provides a key tool for generating arbitrary phonon states in circuit quantum acoustodynamics, which is important for fundamental and quantum information applications

Kerr-enhanced optomechanical cooling in the unresolved-sideband regime

Dynamical backaction cooling has been demonstrated to be a successful method for achieving the motional quantum ground state of a mechanical oscillator in the resolved-sideband regime, where the mechanical frequency is significantly larger than the cavity decay rate. Nevertheless, as mechanical systems increase in size, their frequencies naturally decrease, thus bringing them into the unresolved-sideband regime, where the effectiveness of the sideband cooling approach decreases. Here we demonstrate, however, that this cooling technique in the unresolved-sideband regime can be significantly enhanced by utilizing a nonlinear cavity as shown in the experimental work of Zoepfl et al. [Phys. Rev. Lett. 130, 033601 (2023)]. The above arises due to the increased asymmetry between the cooling and heating processes, thereby improving the cooling efficiency. In addition, we show that injecting a squeezed vacuum into the nonlinear cavity paves the way to ground-state cooling of the mechanical mode. Notably, the required squeezing parameters are far less stringent than in the linear case, simplifying experimental implementation

Generalized non-reciprocity in an optomechanical circuit via synthetic magnetism and reservoir engineering

Synthetic magnetism has been used to control charge neutral excitations for applications ranging from classical beam steering to quantum simulation. In optomechanics, radiation-pressure-induced parametric coupling between optical (photon) and mechanical (phonon) excitations may be used to break time-reversal symmetry, providing the prerequisite for synthetic magnetism. Here we design and fabricate a silicon optomechanical circuit with both optical and mechanical connectivity between two optomechanical cavities. Driving the two cavities with phase-correlated laser light results in a synthetic magnetic flux, which, in combination with dissipative coupling to the mechanical bath, leads to non-reciprocal transport of photons with 35 dB of isolation. Additionally, optical pumping with blue-detuned light manifests as a particle non-conserving interaction between photons and phonons, resulting in directional optical amplification of 12 dB in the isolator through-direction. These results suggest the possibility of using optomechanical circuits to create a more general class of non-reciprocal optical devices, and further, to enable new topological phases for both light and sound on a microchip

Improved upper limb function in non-ambulant children with SMA type 2 and 3 during nusinersen treatment: a prospective 3-years SMArtCARE registry study

Background The development and approval of disease modifying treatments have dramatically changed disease progression in patients with spinal muscular atrophy (SMA). Nusinersen was approved in Europe in 2017 for the treatment of SMA patients irrespective of age and disease severity. Most data on therapeutic efficacy are available for the infantile-onset SMA. For patients with SMA type 2 and type 3, there is still a lack of sufficient evidence and long-term experience for nusinersen treatment. Here, we report data from the SMArtCARE registry of non-ambulant children with SMA type 2 and typen 3 under nusinersen treatment with a follow-up period of up to 38 months. Methods SMArtCARE is a disease-specific registry with data on patients with SMA irrespective of age, treatment regime or disease severity. Data are collected during routine patient visits as real-world outcome data. This analysis included all non-ambulant patients with SMA type 2 or 3 below 18 years of age before initiation of treatment. Primary outcomes were changes in motor function evaluated with the Hammersmith Functional Motor Scale Expanded (HFMSE) and the Revised Upper Limb Module (RULM). Results Data from 256 non-ambulant, pediatric patients with SMA were included in the data analysis. Improvements in motor function were more prominent in upper limb: 32.4% of patients experienced clinically meaningful improvements in RULM and 24.6% in HFMSE. 8.6% of patients gained a new motor milestone, whereas no motor milestones were lost. Only 4.3% of patients showed a clinically meaningful worsening in HFMSE and 1.2% in RULM score. Conclusion Our results demonstrate clinically meaningful improvements or stabilization of disease progression in non-ambulant, pediatric patients with SMA under nusinersen treatment. Changes were most evident in upper limb function and were observed continuously over the follow-up period. Our data confirm clinical trial data, while providing longer follow-up, an increased number of treated patients, and a wider range of age and disease severity

Parametric couplings in engineered quantum systems

Parametric couplings in engineered quantum systems are a powerful tool to control, manipulate and enhance interactions in a variety of platforms. It allows us to bring systems of different energy scales into communication with each other. This short chapter introduces the basic principles and discusses a few examples of how one can engineer parametric amplifiers with improved characteristics over conventional setups. Clearly, the selected examples are author-biased, and other interesting proposals and implementations can be found in the literature. The focus of this chapter is on parametric effects between linearly coupled harmonic oscillators, however, parametric modulation is also applicable with nonlinear couplings and anharmonic systems.</jats:p

Kohärenter Transport durch nanoelektromechanische Systeme

Die Untersuchung von kohärentem Transport durch nanoelektromechanische Systeme (NEMS) steht im Fokus dieser Arbeit. NEMS stellen Bauteile dar, bei denen ein quantenmechanisches Transportsystem an die Freiheitsgrade eines mechanischen Systems koppelt. Damit ist eine Untersuchung der Elektron-Phonon Wechselwirkung in einer Nicht-Gleichgewichtsumgebung möglich. Im Allgemeinen wird bei der semi-klassischen Betrachtung dieser mechanisch-elektrischen Systeme eine adiabatische Näherung durchgeführt. In dieser Näherung geht man davon aus, dass sich die Elektronen die durch das System tunneln deutlich schneller bewegen als der Oszillator, d.h. der Oszillator spürt nur ein effektives von den Elektronen verursachtes Potential, während er seine Position im Gegensatz zu den Elektronen nur langsam verändert. Die interessantesten Phänomene zeigen sich jedoch, wenn sich die Elektronen und der Oszillator sich auf einer ähnlichen Zeitskala bewegen. Im Rahmen dieser Arbeit wird die Dynamik des Oszillators in adiabatischer und in nicht-adiabatischer Näherung untersucht. Um Zugang zu den mechanischen Eigenschaften zu erlangen kann die Methodik der Feynman-Vernon Influenz Funktionale genutzt werden. Wir konzentrieren uns auf zwei elektronische Modellsysteme -- das Ein- und Zwei-Level System -- die linear an eine einzige bosonische Mode koppeln. Wir nutzen den Greenschen Formalismus zur Berechnung der elektronischen Eigenschaften, dieser bietet, in seiner Erweiterung durch Keldysh, Möglichkeiten Nichtgleichgewichts - Prozesse zu beschreiben. Die Dynamik für einen Oszillator im elektronischen Zwei-Level System zeigt ein nicht-triviales Verhalten, es treten beispielsweise Grenzzyklen und Bistabilitäten auf. Wir untersuchen ausführlich die auftretenden Effekte mit Methoden für nichtlineare dynamische Syteme. Zudem erfolgt die Berechnung von Strom und Rauschen, beides Eigenschaften die experimentell zugänglich sind. Eine weitere Besonderheit der verwendeten Methode ist, dass keine störungstheoretische Behandlung der Kopplung zwischen dem Quantensystem und den elektronischen Anschlüssen erfolgt. Zudem zeigen wir, dass sich unsere nicht-adiabatische Methodik ohne weiteres auf bestimmte Systeme übertragen lässt. Dazu nutzen wir das Modell eines elektronischen Transportsystems mit einem elektronischen Level, dass an einen großes Ensemble von Spins koppelt, und dem Einfluss eines externen Magnetfeldes unterliegt. Das Spin Ensemble kann durch einen großen effektiven Spin beschrieben werden, für den eine semi-klassische Beschreibung möglich ist. Dabei werden die Quantenfluktuationen des Systems als klein angesehen und die Wechselwirkung zwischen den Spin- Systemen im Rahmen einer Meanfield-Näherung beschrieben.In this thesis we compare the semiclassical description of nanoelectromechanical systems (NEMS) within and beyond the Born-Oppenheimer approximation. NEMS enable the detailed study of the interaction between electrons, tunneling through a nano-scale device, and the degrees of freedom of a mechanical system. We work in the semiclassical regime where an expansion around the classical path is performed. The advantage of this method is, that it is nonperturbative in the system-leads coupling, because the exact electronic solutions are included. We develop a nonadiabatic approach, where we can treat the oscillator and the electrons on the same time-scale without further constrains. The considered NEMS models contain a single phonon (oscillator) mode linearly coupled to an electronic few-level system in contact with external particle reservoirs (leads). Using Feynman-Vernon influence functional theory, we derive a Langevin equation for the oscillator's trajectories. A stationary electronic current through the system generates nontrivial dynamical behaviour of the oscillator, even in the adiabatic regime. We present a detailed prescription of the oscillator's phase space and investigate the observed dynamical features with methods for nonlinear dynamical systems. The backaction of the oscillator onto the electronic properties is studied as well. For the cases of one and two coupled electronic levels, we discuss the differences between the adiabatic and the nonadiabatic regime of the oscillator dynamics. Furthermore, we apply the developed methods to a single-level system which is anisotropically coupled to a large spin under the influence of an external magnetic field. Here, the semiclassical treatment of the large spin's dynamics is included within a mean-field approach for the spin-spin interaction. This system possess rich dynamical properties, like self-sustained and chaotic oscillations. We investigate the system in the nonequilibrium regime for high external bias, where we can compare our nonadiabatic method to a rate equation approach, which is perturbative in coupling to the leads. Additionally, we study the system in the low bias case, where the dynamics are even richer as in the infinite bias case