Frontiers of quantum computing and sensing: the 10 Sci & Tech questions

2019-11-11 Global Communications

Quantum science and technology is a key research area of 21st century, and may lead to revolutionary advancement in material science and information technology. Over the past decades, quantum information science and technology have witnessed huge achievements, but a continuous effort is still in great demand to move forward the scientific research frontier and develop disruptive applications. Zhejiang University has organized an interdisciplinary discussion and summarized ten key scientific/technological problems in the quest of“Quantum Computing and Sensing”.

1. Is a practical quantum computer superior to the classical counterpart realizable?

Quantum computation can achieve quantum  speedupover the classical counterpart by harnessing quantum algorithms to solve important problems such as large number factorization. Quantum computing prototypes are expected to integrate hundreds of qubits, which can be first used in quantum simulation, and will have a profound impact on the fields of biopharmaceutics, machine learning, artificial intelligence, etc. However, the research and development of a quantum computer and its underlying hardware involve many complex  technological problems in the process of quantum and classical interfacing, such as quantum entanglement, quantum error correction and quantum measurement, which still face great challenges.

2. What is the limit of the decoherence time of solid-state qubits?

Largescale quantum computation and quantum simulation need the integration of many qubits with long coherence time. Improving the coherence of solid-state qubits and approaching the limit of the coherence time will be the key scientific and technological problems of engineering the quantum computer. It needs a better understanding of the mechanism of various kinds of noise and effective methods to increase the coherence time of qubits.

3.How to avoid quantum disturbance?

Conventional computers harness electrical signals for information transmission and processing, which is vulnerable to external electromagnetic radiation, resulting in the reduction of signal integrity. At present, electromagnetic shielding is often used to protect it. As the basic unit of information transmission and processing in a quantum computer, qubit is very vulnerable to the disturbance of the external environment. How to realize quantum shielding and preserve the fidelity of quantum signal is a challenging scientific and technological problem.

4.What is the quantum origin of the chiral molecules?

Biological molecules have certain preference in chirality. However, left-handed and right-handed molecules have the same probability to be generated in chemical reactions. The quantum origin of molecular chirality is an unsolved mystery. From the perspective of quantum mechanics, there are two possibilities for the origin of molecular chirality, namely, interaction that breaks the parity symmetry or quantum decoherence. The formation of chiral molecules can be simulated by an artificially controlled quantum system, which can provide experimental evidences to verify the hypothesis of the origin of chiral molecules.

5.How to achieve the limit of quantum precise measurement?

The ultimate goal of quantum precise measurement is to reach the Heisenberg limit sensitivity which is inversely proportional to the number of particles used in a single measurement.This is far beyond the standard quantum limit that is inversely proportional to the square root of the number of particles in a single measurement when the particle number is large. In fact, it is a frontier research direction of the academic community to develop quantum precise measurement technologies which can be applied in practice and reach the Heisenberg limit.

6. How to realize a quantum superposition state of a macroscopic mechanical oscillator?

Scientists have observed the quantum properties of microscopic particles such as photons, electrons, atoms, molecules, etc. How to observe the quantum behavior of a macroscopic mechanical oscillator and prepare its quantum superposition state is a major challenge in quantum technology.Its study will help to reveal new physical phenomenain the transition regimebetweenthe macroscopic and microscopic worlds, such as the testing of the wave function collapse and other important topics.

7. How to utilize quantum system in high-precision gyroscope?

Gyroscope is a technique to realize navigation and positioning without any external information. The core of its navigation and positioning accuracy is the accuracy of the inertial sensor. Quantum technology is expected to surpass the limit of measurement sensitivity of the classical inertial sensors and improve the accuracy of long-term autonomous navigation and positioning.

8. How to realize accurately controllable single-photon source operating at room temperature?

Quantum communication requires single-photon sources with high single-photon purity (each pulse contains only one photon of the same property) as well as high production efficiency and high extraction rate. It is a great technological challenge to realize a single-photon source with these properties simultaneously. It not onlyis important for the practical application of quantum communication technology, but also has potential applications in weak light measurement and quantum metrology.

9. How small can a laser be?

The momentum of light increases with the spatial constraints, which makes it difficult to prepare the super-constrained coherent optical field. The surface plasmon laser can produce a super-confined coherent light field which is much smaller than the vacuum wavelength. Exploring the limit scale of this kind of laser has promising applications in light-matter interaction, high energy-density light source, precise optical measurement and so on.

10. Is there “Moore-like law” for quantum circuit chips?

Is there a growth expectation similar to Moore's law in computing power of general quantum chips, including quantum entanglement, qubit integration and other core indicators? What kind of mathematical law will be followed to grow every year? What is the limit of the growth?