A Hybrid Atom-Photon-Superconductor Quantum Interface

Lead Research Organisation: University of Strathclyde
Department Name: Physics

Abstract

The field of quantum information arises from a desire to overcome the challenges of solving complex or intractable problems on classical computers by harnessing quantum mechanics to provide efficient and scalable algorithms. Whilst there has been tremendous recent progress in the realisation of small-scale quantum circuits comprising several quantum bits (``qubits''), research indicates that a fault-tolerant quantum computer capable of harnessing the power of quantum mechanics will require a network of thousands of qubits. This goal is presently beyond the reach of any existing implementation based on a single physical qubit type.

Hybrid quantum information processing is an alternative approach that exploits the unique strengths of disparate quantum technologies, and offers a route to overcome the drawbacks associated with of a single-qubit architecture in direct analogy to the design of classical computing hardware. This proposal aims to combine three different technologies:

i) Superconducting circuits, with very fast (10 ns) gate times for fast processing,
ii) Neutral atoms, with long (10 s) coherence times for long lived quantum memory,
iii) Optical photons, for long distance fibre communication,

to create a novel hybrid quantum interface capable of storing, processing and generating highly entangled states of photons for quantum networking and cryptography applications, overcoming the short coherence time associated with the scalable superconducting circuit systems. This also offers applications in quantum metrology for conversion from optical to microwave domain quantum information, making it possible to extend the interface to incorporate a wide range of alternative solid-state based qubits.

The interface relies on use of highly excited Rydberg states, which have incredibly large dipole moments and transitions in the microwave regime, which can resonantly couple to superconducting qubits embedded in planar microwave waveguide cavities. The large Rydberg dipole also leads to strong, controllable interactions between atoms to provide a collective enhancement in the coupling to single photons for efficient storage and retrieval of light.

The first stage of the experiment is to trap spatially addressable atomic ensembles above a superconducting microwave resonator operating at 4 K to demonstrate strong coupling to the waveguide mode, a key milestone for implementing the hybrid interface. The ensembles will then be utilised to perform coherent storage and retrieval of optical photons, as well as generation of single photons using four-wave mixing.

The second stage is to exploit the off-resonant interaction with the cavity to achieve controllable long distance (~1 cm) entanglement between a pair of ensembles trapped within a single microwave resonator. This will then be used to generate entangled photon pairs, exploring the benefits of collective encoding within the ensembles for achieving entanglement in the polarisation degrees of freedom for long-distance cryptographic quantum key distribution. The resulting hybrid quantum interface provides an ideal building block for establishing quantum networks. Long term this can be integrated with existing superconducting qubit technologies, making a significant step towards the realisation of scalable quantum computing.

Planned Impact

1. Academic Impact

This proposal addresses key questions relating to utilising hybrid quantum systems for creating scalable nodes for creation of quantum networks. This work will establish protocols and frameworks for performing high fidelity generation, storage and entanglement of single photons coupled to atomic ensembles trapped above a superconducting circuit, which can be directly translated to existing scalable superconducting qubit technologies.

2. Technological Impact

Quantum technologies (QT) are a rapidly growing area, with key new UK investments including the EPSRC Quantum Technology Network and funding innitiatives from InnovateUK. The proposed research has direct application in development of novel devices for quantum networking, offering a revolutionary new approach to information transfer and enabling large-scale secure networks utilising quantum based encryption as well as offering new limits in precision via quantum metrology.

3. Training

This proposal will produce highly trained personnel at levels from undergraduate to post-graduate, providing an important resource for future academic and commercial development of novel quantum technologies. The specific training in the interdisciplinary fields of atomic physics and superconducting quantum technologies provides a unique skill base.

4. Outreach

Both the PI and Strathclyde Physics department have an established track record in performing outreach to local school children through annual Open Evenings and one-off workshops organised as part of National science week. These activities will be continued with the goal of enhancing the profile of science and particularly novel quantum technologies within the local region.

Publications

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Adams C (2020) Rydberg atom quantum technologies in Journal of Physics B: Atomic, Molecular and Optical Physics

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Chu Y (2021) Hybrid quantum devices: Guest editorial in Applied Physics Letters

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Legaie R (2018) Sub-kilohertz excitation lasers for quantum information processing with Rydberg atoms in Journal of the Optical Society of America B

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Picken C (2017) Single atom imaging with an sCMOS camera in Applied Physics Letters

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Picken C (2018) Entanglement of neutral-atom qubits with long ground-Rydberg coherence times in Quantum Science and Technology

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Šibalic N (2017) ARC: An open-source library for calculating properties of alkali Rydberg atoms in Computer Physics Communications

 
Description We have developed a new experimental platform able to cool and trap individual atoms, with number resolved imaging and the ability to perform quantum gates to enable computation using quantum mechanics instead of classical digital logic used in modern computing. An important step towards this has been building up a set of frequency stable lasers to address atomic transitions to enable the atoms to talk to each other using long range interactions. This opens new avenues for solving complex problems that current computers find hard.

Using this platform we demonstrated the best two-qubit ground-state entanglement of a pair of atoms in 2018, a vital step in developing new hardware for performing computation using quantum mechanics rather than digital logic. This new approach offers efficient solution to computationally hard optimisation problems from factorisation to travelling-salesman style logistics decisions as well as providing new methods for driving material design and drug discovery. We have subsequently demonstrated a new quantum gate protocol offering a scalable approach to multi-qubit gates with neutral atoms.

As part of this work, a new computational library has been developed in association with colleagues at Durham University to enable calculation of the properties of highly excited atomic states that are used to create the quantum states. This has been released open source to the community as a tool for all researchers and has been adopted for use by a number of international groups working in this area.

The final stages of the project have been development of new NbN resonators in collaboration with the grouo of Martin Weides at Glasgow University for coupling single atoms to microwave cavities, offering efficient conversion of photons from the optical to microwave domain and allowing long-range interactions to be generated.
Exploitation Route The next steps of studying how a superconducting circuit can be combined with atomic qubits provides an exciting new approach to building technological devices harnessing quantum mechanics for communication, and could potentially realise a quantum repeater or quantum router that enables extension of the distance over which information can be communicated with single photons or how a network can be built to achieve this, making quantum encryption a reality. This will be of great interest to the telecommunications industry as well as those developing quantum computing architectures, and will demonstrate the success of this new approach.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Security and Diplomacy

URL http://photonics.phys.strath.ac.uk/hybrid/
 
Description Maritime, Enterprise, Innovation and Research Fund
Amount £60,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2017 
End 03/2021
 
Description Scalable Qubit Arrays for Quantum Computing and Optimisation
Amount £2,177,072 (GBP)
Funding ID EP/T005386/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2020 
End 02/2025
 
Title An Introduction to Rydberg atoms with ARC 
Description An example Python notebook demonstrating the ARC:Alkali Rydberg Calculator module functionality which reproduces all data appearing within the published article. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Unknown 
 
Title Data for "Single Atom Imaging with an sCMOS camera" 
Description Single atom imaging requires discrimination of weak photon count events above background and has typically been performed using either EMCCD cameras, photomultiplier tubes or single photon counting modules. sCMOS provides a cost effective and highly scalable alternative to other single atom imaging technologies, offering fast readout and larger sensor dimensions. We demonstrate the first single atom resolved imaging of two site-addressable single atom traps separated by 10 ?m using an sCMOS camera, offering a competitive signal-to-noise ratio at intermediate count rates to allow high fidelity readout discrimination (error < 10?6) and sub-?m spatial resolution for applications in quantum technologies. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Unknown 
 
Title Data for: "Entanglement of neutral-atom qubits with long ground-Rydberg coherence times" 
Description This dataset contains all Excel data presented in the paper "Entanglement of neutral-atom qubits with long ground-Rydberg coherence times". The paper presented results of a ground-state entanglement protocol for a pair of Cs atoms separated by 6~?m, combining the Rydberg blockade mechanism with a two-photon Raman transitions to prepare the |?+?=(|10?+|01?)/2?? Bell state with a loss-corrected fidelity of 0.81(5), equal to the best demonstrated fidelity for atoms trapped in optical tweezers but without the requirement for dynamically adjustable interatomic spacing. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact
 
Title Sub-kHz linewidth lasers for Quantum Information Processing with Rydberg atoms 
Description Quantum information processing using atomic qubits requires narrow linewidth lasers with long-term stability for high fidelity gate operations. In this paper, we report on the construction and characterization of three continuous-wave (CW) narrow linewidth lasers stabilized simultaneously to an ultra-high finesse Fabry-Perot cavity made of ultra-low expansion (ULE) glass, with a tunable offset-lock frequency. One laser operates at 852 nm while the two locked lasers at 1018 nm are frequency doubled to 509 nm for excitation of 133Cs atoms to Rydberg states. The optical beatnote at 509 nm is measured to be 260(5) Hz. We present the calibration of ULE cavity frequency with respect to atomic resonances using electromagnetically induced transparency (EIT) for high-resolution spectroscopy on a cold atom cloud. The long-term stability is determined from repeated spectra over a period of 20 days and is found ~ 1 Hz/s. Readme file contains file format information for zipped datasets. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Unknown 
 
Description M Squared Lasers 
Organisation M Squared Lasers Ltd
Country United Kingdom 
Sector Private 
PI Contribution We have provided access to the UK's only two-qubit atomic tweezer experiment along with expertise in coherent control and stabilisation to an ultra-stable reference cavity to aid development of new locking techniques for M Squared Lasers main laser system.
Collaborator Contribution M Squared provided a high-power frequency doubled laser system to advance our capability in driving fast two-photon excitation of atomic qubits and to work with us in developing laser stabilistation techniques.
Impact This collaboration has led to submission of a Prosperity Partnership proposal to develop a new scalable quantum computer based on neutral atoms.
Start Year 2019
 
Title ARC (Alkali Rydberg Calculator) 
Description ARC (Alkali Rydberg Calculator) is an open-source package of routines written in Python, using object-oriented programming (OOP) to make modular, reusable and extendable collection of routines and data for performing useful calculations of single atom and two-atom properties, like level diagrams, interactions and transition strengths for alkali metal atoms. 
Type Of Technology Software 
Year Produced 2017 
Open Source License? Yes  
Impact This software, developed in collaboration with researchers at the University of Durham, has had a big impact within the field of Rydberg physics which is currently been downloaded and used by over 30 groups from 20 different countries to our knowledge. 
URL https://www.sciencedirect.com/science/article/pii/S0010465517301972?via%3Dihub
 
Description Glasgow Science Festival 2016 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact A stand displaying the benefits of new quantum technologies including a live interactive demonstration of laser cooling was presented at a two-day event a the Kelvingrove Museum as part of Glasgow Science Festival. During this time we had around 100 members of the public aged from 5-80 engaging with our exhibit, learning about how the quantum technology investments will lead to new technologies that will impact daily life.
Year(s) Of Engagement Activity 2016
URL http://www.glasgowsciencefestival.org.uk
 
Description Progress towards a hybrid Atom- Superconductor Interface for Quantum Networking 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Progress towards a hybrid Atom- Superconductor Interface for Quantum Networking
Year(s) Of Engagement Activity 2018
 
Description QUISCO 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Progress towards a hybrid atom-superconductor interface for quantum networking
Year(s) Of Engagement Activity 2017
 
Description Radio Interview following announcement of QT Fellowships 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Media (as a channel to the public)
Results and Impact Interview for radio Clyde promoting the announcement of the QT fellowship awards and specifically the main aims and objectives of the project. Broadcast throughout the day on Radio Clyde 1 and Clyde 2 (regional Glasgow radio).
Year(s) Of Engagement Activity 2015
 
Description School Visit (Lairsland Primary) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Prepared a series of hands-on activities to introduce a class of 25 children to the science that underlies the technology being developed through this research. Students given a chance to explore activities and ask lots of questions to stimulate interest in science.
Year(s) Of Engagement Activity 2015