Microwave Quantum Link between Superconducting Circuits Housed in Spatially Separated Cryogenic Systems.

Superconducting circuits are a strong contender for realizing quantum computing systems and are also successfully used to study quantum optics and hybrid quantum systems. However, their cryogenic operation temperatures and the current lack of coherence-preserving microwave-to-optical conversion solutions have hindered the realization of superconducting quantum networks spanning different cryogenic systems or larger distances. Here, we report the successful operation of a cryogenic waveguide coherently linking transmon qubits located in two dilution refrigerators separated by a physical distance of five meters. We transfer qubit states and generate entanglement on demand with average transfer and target state fidelities of 85.8% and 79.5%, respectively, between the two nodes of this elementary network. Cryogenic microwave links provide an opportunity to scale up systems for quantum computing and create local area superconducting quantum communication networks over length scales of at least tens of meters.

Fast and Unconditional All-Microwave Reset of a Superconducting Qubit.

Active qubit reset is a key operation in many quantum algorithms, and particularly in quantum error correction. Here, we experimentally demonstrate a reset scheme for a three-level transmon artificial atom coupled to a large bandwidth resonator. The reset protocol uses a microwave-induced interaction between the |f,0⟩ and |g,1⟩ states of the coupled transmon-resonator system, with |g⟩ and |f⟩ denoting the ground and second excited states of the transmon, and |0⟩ and |1⟩ the photon Fock states of the resonator. We characterize the reset process and demonstrate reinitialization of the transmon-resonator system to its ground state in less than 500 ns and with 0.2% residual excitation. Our protocol is of practical interest as it has no additional architectural requirements beyond those needed for fast and efficient single-shot readout of transmons, and does not require feedback.

Deterministic quantum state transfer and remote entanglement using microwave photons.

Sharing information coherently between nodes of a quantum network is fundamental to distributed quantum information processing. In this scheme, the computation is divided into subroutines and performed on several smaller quantum registers that are connected by classical and quantum channels 1 . A direct quantum channel, which connects nodes deterministically rather than probabilistically, achieves larger entanglement rates between nodes and is advantageous for distributed fault-tolerant quantum computation 2 . Here we implement deterministic state-transfer and entanglement protocols between two superconducting qubits fabricated on separate chips. Superconducting circuits 3 constitute a universal quantum node 4 that is capable of sending, receiving, storing and processing quantum information5-8. Our implementation is based on an all-microwave cavity-assisted Raman process 9 , which entangles or transfers the qubit state of a transmon-type artificial atom 10 with a time-symmetric itinerant single photon. We transfer qubit states by absorbing these itinerant photons at the receiving node, with a probability of 98.1 ± 0.1 per cent, achieving a transfer-process fidelity of 80.02 ± 0.07 per cent for a protocol duration of only 180 nanoseconds. We also prepare remote entanglement on demand with a fidelity as high as 78.9 ± 0.1 per cent at a rate of 50 kilohertz. Our results are in excellent agreement with numerical simulations based on a master-equation description of the system. This deterministic protocol has the potential to be used for quantum computing distributed across different nodes of a cryogenic network.

Distensibility and responsiveness of the rat seminal vesicle: effects of denervation and pretreatment of animals with 6-hydroxydopamine and reserpine.

Slow filling (0.03 ml/min) to 25 cm H2O transluminal hydrostatic pressure established an internal volume ("end-filling volume"; V) in rat seminal vesicles which was optimal for the production of maximal isovolumetric contractions. Because of variations in the size and empty wet weight (W) of vesicles from mature rats, this method for standardizing base-line conditions was superior to the application of a standard volume to preload all organs. The slow-filling procedure to establish base-line conditions yielded a parameter (V/W) which was an index of organ distensibility; therefore, both mechanical and pharmacological properties could be related in each organ. V/W was reasonably constant and independent of organ weight; regression analysis showed K = V/W3/4. Pretreatment of animals with 6-hydroxydopamine. HBr (100 mg/kg 2 weeks, plus 50 mg/kg 1 week, before sacrifice) and surgical postganglionic denervation (9 to 12 days before sacrifice) significantly increased V/W, had no effect on W and resulted in a 40% increase in the maximum response to norepinephrine. The EC50 of norepinephrine was slightly increased after 6-hydroxydopamine-pretreatment. Short-term reserpine-pretreatment (5 mg/kg 2 days plus 2.5 mg/kg 1 day, before sacrifice) produces better norepinephrine depletion than 6-hydroxydopamine but did not modify V/W. The results suggest that the stress-strain relationship and elastic properties of sympathetically innervated tissues are subject to the long-term influence of nerve activity.

Motor innervation of the smooth muscle of the rat seminal vesicle.

Frequency-related isovolumetric contractions of the rat seminal vesicle elicited with transmural electrical stimulation were blocked by tetrodotoxin but unaffected by hexamethonium. The postganglionic motor innervation of the rat seminal vesicle is purely excitatory and contains both an adrenergic and a cholinergic component which are excited simultaneously during transmural stimulation. Contractions elicited by adrenergic nerve stimulation were mediated by norepinephrine acting via alpha adrenoceptors, i.e., 1) responses of untreated vesicles to transmural stimulation and to exogenous norepinephrine were antagonized by phentolamine and potentiated by cocaine, 2) pretreatment of animals with reserpine or 6-hydroxydopamine produced a marked depletion of tissue norepinephrine concentration and reduced the responses to transmural stimulation to a level which resembled that of untreated organs in the presence of phentolamine, 3) the residual responses of vesicles from pretreated rats were not modified by phentolamine or cocaine, and 4) responses to tyramine in untreated organs were antagonized by phentolamine but not by cocaine and were observed in organs from reserpine-pretreated rats only after repletion with exogenous norepinephrine. Responses elicited by cholinergic nerve stimulation were mediated by acetylcholine through muscarinic receptors, i.e., 1) responses of untreated vesicles to transmural stimulation and to exogenous acetylcholine were antagonized by atropine, 2) the residual responses to transmural stimulation of vesicles from animals pretreated with reserpine of 6-hydroxydopamine were nearly abolished by atropine and 3) physostigmine potentiated and prolonged the responses of organs from untreated and reserpine-pretreatd animals to transmural stimulation; these effects of physostigmine were abolished by atropine.

Dissociation constants and relative efficacies of agonists acting on alpha adrenergic receptors in rabbit aorta.

The dissociation constants (KA values) of l-norepinephrine (l-NE) and seven other agonists acting on alpha adrenergic receptors in rabbit aorta strips were determined by analysis of concentration-response data before and after fractional inactivation of receptors with Dibenamine. In experiments to determine KA values, propranolol was added to block activation of beta receptors and cocaine to block the neuronal uptake mechanism. The KA of l-NE and the KA of a second agonist, when determined on paired strips from the same aorta, were used to calculate the relative affinity and the relative efficacy (er) of the second agonist as compared to l-NE. The validity of the method used for determining KA and er values was supported by the following findings. 1) The dissociation constant (KB) of the competitive antagonist, phentolamine, determined with each of the agonists, was the same as that determined with l-NE. 2) The KA determined for l-NE was independent of the fraction of active receptors remaining (q) after pretreatment with different concentrations of Dibenamine. 3) The KB of phentolamine determined with l-NE as the agonist was the same before and after fractional inactivation of receptors. 4) After inactivation in paired strips by equal exposures to Dibenamine, the q value determined with each agonist was the same as that determined with l-NE. The mean KA value for l-NE was 3.39 +/- 0.15 X 10(-7) M. The mean relative affinities of the agonists for the alpha receptor were: l-NE, 1;L-EPINEPHRINE, 1.25; L-PHENYLEPHRINE, 0.200; L-norphenylephrine, 0.217; epinine, 0.136; dopamine, 0.0055; l-alpha-methylnorepinephrine, 0.095; dl-alpha-ethylnorepinephrine, 0.0048. The mean er of each agonist was not significantly different from that of l-NE, except for l-norphenylephrine with an e of 0.71, and dl-alpha-ethylnorepinephrine with an er of 0.41. The results are discussed from the standpoint of structure-activity relationships.