Towards Real Applications in Broadband Quantum Memories

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


Imagine a banknote that cannot be forged, because the serial number is scrambled every time someone tries to read it. But if you are the banker, you can read it. Sounds like Harry Potter? Imagine a computer that predicts how drugs will behave by simulating all possible chemical reactions at once! This is not an idea from Phillip Pullman's fantasy of parallel universes. Real technologies like this are just around the corner.

This is the fascinating, counter-intuitive world of quantum physics. Huge advances in communications and computing technology over the last several decades have made this the information age and changed the way people live and interact even more drastically than did the industrial revolution. These advances have piggy-backed on the development of devices such as semiconductor transistors and lasers, devices which wouldn't be possible without the weird properties of quantum physics.

But although modern computers have far-outstripped the early technology of punch cards and vacuum tube valves, at an underlying conceptual level, they still use exactly the same type of information - strings of 0s and 1s called bits. Quantum physics will allow us go far beyond this into the strange world of quantum information, where the "quantum bits" can be both 0 and 1 simultaneously! Computers that could work with this sort of information would be exponentially faster at performing difficult simulations or cracking codes. And communicating using quantum information can be made "eavesdropper proof" - perfectly secure.

Over the past ten years, an enormous research effort has brought these extraordinary technologies from abstract ideas to small-scale experiments. One of the most promising ways to build a quantum computer is based on single particles of light, called photons, which can be sent over long distances in optical fibres and manipulated with ordinary lenses and mirrors. But like normal computers, quantum computers need memories to be able to synchronise different parts of a computation by storing the quantum information until it is needed. So to build a photonic quantum computer, we also need to have a quantum memory that can store single photons. What makes this difficult is that these special memories need to be able to store the fragile quantum information without destroying or even "looking" at it (measuring it).

In this project, we will develop a quantum memory for photons which can store short pulses for long times with high efficiency and very low noise. To do this, we will use a "Raman memory", an approach pioneered in our group which uses a strong laser pulse to cause the photon to be absorbed by a sample of atoms which is normally transparent. Because the absorption is created by the strong laser (which is not absorbed), there is no noise from excited atoms, and the atoms don't need to be specially prepared by cooling them or trapping them.

The simplicity of our design will allow us to build the first practically feasible memory, which would even potentially be capable of operating in isolated, harsh environments, such as on the ocean floor. This will also allow us to perform novel photonics experiments which are too complex to operate without the memory. We will also develop a miniaturized memory that could be mass-produced and integrated with existing telecoms fibres. Such a device will do for quantum photonics what the transistor did for conventional electronics.

Quantum memories will open the way to a new era of quantum enabled devices, with super-fast computers, perfectly secure communications and ultra-precise measurements. Our research is the key to bringing these truly magical technologies to life.

Planned Impact

Quantum memories are vital to quantum networks. If quantum communications make up just 3% of the UK telecoms industry alone in the future, quantum memories will be the enabler of a market worth over a billion pounds annually. Quantum memories are also crucial if LOQC is to become viable. Key to the development of quantum computers, good quantum memories would pave the way for a novel and disruptive industry with global impact. Quantum computers offer exponential speed-ups over classical devices, perhaps most notably in the solution of systems of linear equations. This operation is so ubiquitous in numerics that nearly all computations would enjoy exponential acceleration. The practical and commercial benefits of realising such a device justify research on quantum memories as a matter of urgency.

These possible applications illustrate that quantum memories could underpin a technology revolution which will have a transformative impact on our ever-more-information-based society, both economically and in changing the way we live. The key road-block to the realization of this potential is practicality: to date, the most successful quantum memories rely on prohibitively complex apparatus such as atom traps and cryogenics. By contrast, the proposed project will develop a technically simple quantum memory requiring no cryogenics or complex alignment which is compatible with integrated optics using state-of-the-art solid-state or hollow-core waveguide technologies. Even now our memory provides competitive or world-leading performance by comparison with other memories. But technical simplicity will be crucial for any memory to support a scalable QIP architecture, and our memory is by far the simplest protocol. We are currently the only research group worldwide pursuing this approach, which places us in a prime position to capitalize on intellectual property and industrial development possibilities. The economic and societal benefits to the UK of being in a leading position for developing the key enabling device for quantum computation and communication will be profound.

The first-stage beneficiaries will be those in academia, but this will have some indirect non-academic benefits. For example, the question of building an industry-compatible memory has to date mostly been overlooked. Addressing this issue is a key aim of our research and our publications will stimulate the research community in moving towards a more operational approach. This will build momentum towards realising a global quantum network, with important impacts outside the academic community.

The second-stage beneficiaries include non-academic industrial and commercial sectors, and indeed society as a whole. Firstly, global quantum networks would provide unconditionally secure communication based on quantum key distribution. Since most transactions are processed over the internet (eg, banking, retail, stock-market, etc), this technology will revolutionise security for nearly all monetary transactions and would have an enormous impact on the global economy. With cybercrime and identity theft now threatening everyone, this would have a tangible impact on people's quality of life. Further, unconditionally secure communication would have a major impact on the effectiveness of intelligence services in combating terrorism.

Secondly, quantum computers enabled by our quantum memories would have a great impact in many fields. For example, quantum simulations would transform methods of research and commercialization in the health, pharmaceuticals and green energy energy sectors. It would assist epidemiology and genetic research, cut costs in drug design, and help improve alternative energy sources, for example by permitting simulations of efficient photosynthesis. Indeed, it will have an impact in any area requiring innovation at the molecular scale, where classical computers are ineffectual and time-consuming, expensive empirical testing is currently the only option.


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Vidrighin M (2013) Requirements for two-source entanglement concentration in Quantum Measurements and Quantum Metrology

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Thomas S (2017) High efficiency Raman memory by suppressing radiation trapping in New Journal of Physics

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Spring JB (2013) Boson sampling on a photonic chip. in Science (New York, N.Y.)

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Saunders DJ (2016) Cavity-Enhanced Room-Temperature Broadband Raman Memory. in Physical review letters

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Nunn J (2013) Enhancing multiphoton rates with quantum memories. in Physical review letters

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Nicolle M (2021) Gigahertz-bandwidth optical memory in Pr3+:Y2SiO5. in Optics letters

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Michelberger P.S. (2014) Heralded single photon storage in a room-temperature, broadband quantum memory in Optics InfoBase Conference Papers

Description We have developed a unique approach to the storage and retrieval of quantum light in ensemble quantum memories. We have demonstrated efficient and low-noise memory operation in an atomic gas (Cs), including operation of the memory as a light-matter beamsplitter. Also, we have used the protocol to demonstrate the entanglement of two room-temperature solid-state samples - diamond, in fact.
Exploitation Route We are engaged with ISIS Innovation, the Oxford University Technology Transfer company to identify possible patentable and licensable technology. Our diamond work has been in partnership with Element6, a UK-based manufacturer of industrial diamonds. Possible options for using our unique spectroscopy to distinguish between different types of diamonds have been considered. We are collaborating with several partners to realise memory operation in the truly quantum regime.

Note added (Feb 2020); The ORCA protocol has been patented, and a license is in negotiation with a start up company.
Sectors Digital/Communication/Information Technologies (including Software)

Description This research has generated a number of publications that have appeared in high-impact journals and generated some media coverage. This has added to the recent "buzz" around quantum technologies which has resulted in the award of a very large grant focussed on bringing quantum technologies to market through industry engagement. It is difficult to assess the economic impact at this stage but there is now an opportunity to develop commercial devices. Note added (Feb 2020); Further work on the outcomes of this project were taken forward under the UK Quantum Technology Programme, and a license for the ORCA patent is being discussed with a spin out from the University of Oxford, ORCA Computing. (
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Economic

Description Towards Deterministic Photonic Entanglement Using Time-Frequency Control
Amount $120,000 (USD)
Funding ID FA9550-17-1-0064 
Organisation Airforce Office of Scientific Research 
Sector Public
Country United States
Start 12/2016 
End 12/2019
Description Element 6 
Organisation De Beers Group
Department Element Six
Country Luxembourg 
Sector Private 
PI Contribution Identifying the need for high nitrogen impurities for our quantum memory project.
Collaborator Contribution Providing these diamonds.
Impact No outputs as of yet.
Start Year 2013
Description Paderborn 
Organisation University of Paderborn
Country Germany 
Sector Academic/University 
PI Contribution Characterization of spontaneous parametric down-conversion in multiple waveguides on a single periodically-poled KTP chip.
Collaborator Contribution Advice concerning development of a heralded photon source built with a waveguide in periodically-poled KTP.
Impact Preliminary studies of photon-pair generation in KTP waveguides at Oxford.
Start Year 2013
Description A quantum memory device includes an atomic ensemble (4) and a signal source of electromagnetic radiation (10) for generating modes to be stored and having a frequency corresponding to an off-resonant transition between first and second states in the atomic ensemble. The quantum memory device also includes a control source of electromagnetic radiation (12) for generating electromagnetic radiation having a frequency corresponding to an off-resonant atomic transition between second and third states in the atomic ensemble; the third state has a higher energy than the second state which has a higher energy than the first state. The signal source and the control source create a coherent excitation of the transition between the first state and the third state such that the atomic ensemble stores the signal source modes, and the control source subsequently stimulates emission of the stored modes from the atomic ensemble. 
IP Reference WO2017212212 
Protection Patent granted
Year Protection Granted 2017
Licensed No
Impact none