We are about to enter a new transitional phase in the development of quantum technology. Behind the headlines there are a diversity of strategies available for those wanting to get on board.
In 2012 Caltech professor John Preskill coined the term quantum supremacy for the quest to demonstrate a calculation on a quantum device that is not practical on any conventional computer. Many think Google will soon achieve this eye catching milestone, though probably on a rather artificial problem. In reality we are still many years, perhaps decades, away from the ultimate goal of building a fault tolerant universal quantum computer. Preskill has just coined a new name for the transitional period we are about to enter – the era of noisy intermediate-scale quantum technology, NISQ. What will it be like?
Quantum hardware announcements continue to come at gathering speed. Alibaba, Rigetti, Intel, IBM and now Google have announced chips variously between 11 and 72 qubits. The reality is that these devices are still all very limited in their capabilities. Leading qubit technologies allow quantum gates to be implemented with seemingly impressive fidelity (error rates less than 1%). However over a large calculation, the impact of such ‘faults’ builds-up. At some point this ‘noise’ will cause the calculation to fail.
In theory, once the error rate is below a threshold of 1% we know how to correct errors dynamically to perform fault tolerant quantum computation. However the best current techniques come with an incredibly high overhead in the number of physical qubits required. The details vary by application, but implementing 4000 perfect logical qubits might require 6 million physical qubits, all while maintaining performance and control of the fragile quantum system.
The flagship race in the NISQ era will be for groups seeking to win this marathon race to create a large scale, programmable, fault tolerant, universal quantum computer. Many believe such a device will unlock remarkable capabilities.
It will be a long and very expensive programme. Groups and technologies that seem to have the advantage now, may not necessarily last the pace. This hardware is the natural domain of big tech and specialist start-ups. It could still be that winning will involve the mobilisation of a nation-state level effort, as is now getting underway in China.
Principally this journey is an inward looking series of technical challenges. Application and industry specific insight is not at its heart. However the major players will still seek wider engagement. If we follow the history of conventional digital tech, it may turn out that the battle to set standards in software is equally influential and lucrative in the long term. Players are already trying to build a user base and eco-system around their offerings for this coming battle.
However this won’t be the only activity in the NISQ era.
Track & Field
NISQ devices will not be capable of implementing full scale ‘textbook’ quantum algorithms. However the question naturally arises – if we forego the implementation of formal error correction and all the overhead that entails, can we still squeeze out some useful calculations from these early devices? Are there cut-down applications that might prove more noise tolerant than others? Might heuristic approaches achieve useful practical results? The truth is we don’t know. This is likely to be settled by experimentalists and early adopters, not theory.
Many groups will choose to try their hand across disparate opportunities of this type: tweaking their device and control software to maximise bespoke performance, developing ‘low depth’ algorithms that require only a minimum number of gate logic steps, targeting applications that have natural resilience to some noise remaining in the process.
These initiatives are likely to tackle problems across a range of commercially interesting areas: optimisation problems (logistics, financial portfolios), deep learning (AI), quantum chemistry (pharmaceuticals R&D). No one knows what progress will be possible with NISQ technology.
Different qubit technologies and device configurations will compete in parallel for different niches in this landscape. Such initiatives are likely to be entrepreneurial and innovative in character, working to shorter timelines and willing to fail quickly when it is necessary to draw lessons. Involvement from other application-specific disciplines (chemistry, materials science, financial quants) and industry is likely to be important. Even where projects fail, participants are likely to see real benefits from the development of their staff and their team’s ability to engage with the next opportunity.
Importantly the model of quantum computing assumed above (the circuit model) is not the only approach to quantum computation. Others are already setting out in other directions.
The NISQ era may be a golden age for quantum simulators (not to be confused with the task of simulating quantum algorithms on conventional computers, quantum simulators are real quantum systems but used as a direct analogue to a problem – something like an old fashioned slide rule, if you can remember one of those). In the first instance they can be used to model the physics and chemistry of less accessible systems, however they also have potential application to more abstract problems. Current work by Jose Rosales and Vicente Martin on integer factorisation using a Penning ion trap is an interesting example of what might be possible. Where approaches of this sort work they could be very disruptive, they may sit outside of timelines and constraints otherwise commonly discussed.
D-Wave Systems is the leading exponent of another major approach: quantum annealing. This can itself be seen as a noisy intermediate-scale step on the path to what is known as adiabatic quantum computing. While the theoretical underpinnings of this roadmap are less well understood, it has the advantage of a growing and active user base. Fresh from securing its latest tranche of investment funding, D-Wave is continuing to augment the capabilities of its hardware with more control over the annealing process.
These alternative approaches offer another way for shorter term projects to seek advantage now from these new technologies. A premium will lie on the mathematical skill and innovation of staff able to map industry challenges onto these novel methods of calculation.
The modern pentathlon
Computation is far from being the only thing that can be done with quantum technology in the NISQ era. The same underlying technological developments imply continuing and significant steps forward in related areas.
The raised awareness of the NISQ era will draw attention to the need for companies to start to act now to prepare for the adoption of quantum safe cryptography. It will also greatly enhance the capabilities of one of our tools for that response: quantum cryptography. First generation systems are already available from companies such as IDQ, Toshiba and QuantumCTek. The NISQ era will refine these technologies. We can expect to see quantum repeaters that overcome the current distance limitations on optical fibre based quantum key distribution (QKD). More advanced entanglement based QKD protocols will become practical, enhancing the robustness of the security promise.
Suppliers are already seeking lead adopters for proof of concept QKD trials. We can expect to see early adopters, especially in the sensitive finance and health sectors, exploiting such initiatives in their marketing and brand development.
Quantum sensing applications will also benefit from the continued hardware developments of the NISQ era. The amazing sensitivity of this new family of magnetic, gravitational, inertial, timing and imaging sensors is ultimately derived from the deployability and fidelity of very similar technology.
A wide range of quantum sensing devices are just reaching commercial prototype deployment across a range of sectors (including resource exploration, civil engineering, medical devices and defence). Awareness of the potential impact of these devices is likely to grow rapidly. Many businesses will find this a straightforward and low risk way to start to benefit directly from quantum technology.
Topping the medal table
To date the headline race to create a universal quantum computer has commanded most attention, and it is an epoch defining goal. However the NISQ era will provide a wide variety of alternative paths for both specialists and the wider business community to follow. We can expect a growing cascade of activity. The contribution of entrepreneurs and industry early adopters will be felt most strongly away from the headline race. Nation states will increasingly take notice of how they can help their businesses and citizens develop themselves for success across these opportunities.
There will be many failures, it will take time. In the end there will be great success.