This project seeks to develop next-generation hardware for quantum networking by using atomic ensembles coupled to superconducting microwave circuits to generate, store and entangle photons in a single chip-based device. This offers a direct route to the creation of scalable quantum networks, in addition to future integration with ultra-fast superconducting qubits to enable distributed quantum computing.
Hybrid systems offer an alternative route to fulfilling the requirements for quantum information processing by combining disparate technologies, in this case neutral atoms and superconductors. Using established techniques of laser cooling and magnetic trapping, atoms will be manipulated above the surface of a superconducting circuit. When the atoms are excited to high-lying Rydberg states, the large dipole moments lead to strong long-range interactions which ensure only a single excitation is created, which enables single photon generation. Interestingly, these interactions lead to the creation of collective states offering an enhanced atom-photon coupling strength in addition to highly directional emission for efficient coupling between single photons and optical fibres. Finally, long range entanglement between atomic ensembles can be achieved using a cavity mediated long-range interaction. Using such a system, it should be possible to generate arbitrary entangled states between multiple optical modes as a first step towards a quantum router, a key building block for scalable quantum networking.
Experimental setup uses high NA lenses to create microscopic dipole traps for trapping atoms into a single blockade volume and manipulating close to the surface for a superconducting microwave coplanar waveguide resonators. Atoms are cooled in a room temperature vapour cell and transported ~ 30 cm in an optical dipole trap into the 4 K cryostat, acting as a dense reservoir for efficient loading of the micro traps.
- R. Legaie, C.J. Picken and J.D. Pritchard, Sub-kHz excitation lasers for Quantum Information Processing with Rydberg atoms, J. Opt. Soc. B 35, 892 (2018) [arXiv].
- C.J. Picken, R. Legaie and J.D. Pritchard, Single atom imaging with an sCMOS camera, Applied Physics Letters 111, 164102 (2017) [arXiv].
- N. Šibalić, J.D. Pritchard, C.S. Adams and K.J. Weatherill, ARC: An open-source library for calculating properties of alkali Rydberg atoms, Computer Physics Communications 220, 319 (2017). See atomcalc.jqc.org.uk.
180327 – Rydberg Rabi Oscillations
Coinciding with publication of our paper detailing our sub-kHz Rydberg excitation lasers in JOSA B we have seen our first coherent single-atom Rabi oscillations between 6S1/2 |F=4,mF=4> and 49D5/2 mj=3/2. Following optimisation of the alignment and polarisations, we are now ready to entangle our atoms.
180215 – Ground-state Rabi Flopping and Ramsey Spectrscopy
We have performed ground-state rotations from |4,0> to |3,0> using a two-photon transition detuned 120 GHz from the D2 excited state to minimise decoherence from spontaneous emission. Data below show Ramsey fringe measurements for two pi/2 pulses separated by a time T. Fitting the full time series we obtain an initial coherence time of 2 ms. We plan to improve this using a magnetic dressing technique (see PRA 81, 041805 (2010)).
171108 – New paper on the arXiv – Sub-kHz excitation lasers for QIP with Rydberg atoms
New paper detailing our Rydberg excitation lasers. We stabilise 3 lasers to the same high finesse cavity made from ultra-low expansion (ULE) glass, allowing us to lock two independent Rydberg excitation lasers to the cavity simultaneously. These lasers are then frequency doubled to 509 nm, and we measure a linewidth of 130 Hz in the green, meaning <100 Hz for the IR master lasers. Using temperature tuning we are able to minimise the linear thermal expansion coefficient of the glass and demonstrate a long term drift of ~ Hz/s when measured against transitions to the 50S1/2 Rydberg state in cold atoms. This meets the requirements for narrow linewidth and low drift required for high-fidelity quantum gates with Rydberg atoms.
170905 – New paper on the arXiv – Single atom imaging with an sCMOS camera
First results from the lab showing single atom measurement errors <10-6 level, giving high fidelity readout of qubits in the two atom traps using a newly developed camera technology that is well suited to building large scale arrays of atomic qubits.
170614 – Single atom imaginge
We now have two single atom traps giving us the first addressable atomic qubits in Scotland! Video below shows the two traps separated by 15 microns – we load with 60% efficiency, making it possible to see the blinking of the sites and can image with >98% retention, ideal for high fidelity qubit readout.
170608 – Atoms in Microscopic Dipole Trap
Atoms transferred from 1064 transport ODT to 1.5 um microscopic dipole trap. Image below shows ~ 10 atoms loaded into trap.
170402 – Upgraded mechanical stage transport
Following thermal instability and lack of reproducibility of focus adjustable lenses we have upgraded to mechanical transport stage enabling much tighter trapping potential
170320 – Cold Atom EIT
Calibration of ULE cavity mode frequencies with respect to Rydberg transition using cold atom EIT
161216 – ARC: Alkali Rydberg Atom Calculator Released
Open-source python library for calculating properties of Alkali Rydberg atoms developed with Nikola Sibalic, Charles Adams and Kevin Weatherill at JQC in Durham. Full details on the arXiv:1612.05529 – download source from GitHub or use the online Atom Calculator by following the link below.
160520 – Cold Cs Atoms
Magneto-Optical Trap (MOT) finally up and running in the first stage chamber at room temperature. Atoms are loaded from background vapour and will then be transported in a moving 1064 nm dipole trap to the cold region above.
160225 – First Rydberg EIT in Scotland
Two-photon excitation of thermal Cs atoms from 6S1/2 ground state to the 63D5/2 state using light at 852 nm and 509 nm from the homebuilt SHG system.
151019 – Optical Tables Arrived
Dr. Jonathan Pritchard
Felix Hoffet – UG Project: Microwave sensing with EIT using dispersive readout
Ilian Despard – UG Project: Construction of Rydberg laser SHG system for microwave sensing with EIT
Sukhpal Singh – UG Project calculating finite temperature effects in hybrid quantum systems