Chinese Scientists Make Breakthrough in Quantum Computing

[JSCh]

Scientists Realize High-Fidelity Single-Qubit Gates on Neutral Atoms
Dec 14, 2018

Prof. ZHAN Mingsheng’s group from Wuhan Institute of Physics and Mathematics (WIPM) of Chinese Academy of Sciences recently made progress in quantum information processing with optically trapped neutral atoms. Utilizing the magic-intensity optical trapping technique, they constructed a novel atomic quantum register, in which the fidelity of global single-qubit gates was achieved higher than 99.99% for the first time.

This fidelity surpasses the commonly accepted error threshold per gate ( 10-4) for quantum fault tolerance computation. This work was published in the Journal of Physical Review Letters.

Neutral atoms in optical dipole trap (ODT) arrays, when serving as quantum bits (qubits), are believed to have outstanding scalability for quantum simulation and quantum computation. As a conventional approach, ODT arrays with linear polarization have been widely used to assemble neutral-atom qubits for building a quantum computer.

However, due to the inherent scalar differential light shifts (DLS) of qubit states induced by trapping fields, the microwave-driven gates acting on single qubits suffer from errors on the order of 10-3. It is thus crucial to construct such an ODT array in which the detrimental DLS of qubits can be effectively compensated so that one can implement high performance microwave-driven gates with errors per gate bellow 10-4.

In this study, researchers constructed a DLS compensated ODT array based upon a recently developed magic-intensity trapping technique. In such a magic-intensity optical dipole trap (MI-ODT) array, the detrimental effects of DLS are efficiently mitigated so that the performance of global microwave-driven Clifford gates is significantly improved.

Experimentally, they achieved an average error of (4.7±1.1)× 10-5 per global gate, which is characterized by randomized benchmarking in a 4×4 MI-ODT array.
The results showed that MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.

This study, together with their previous demonstration of the coherent transfer of a mobile qubit and the entanglement of two individual atoms of different isotopes via Rydberg blockade, represents key steps towards a scalable quantum computer with neutral atoms trapped in MI-ODT arrays.

This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China and the Strategic Priority Research Program of the Chinese Academy of Sciences.

Array experiments. (a) The 4*4 profiels of MI-ODT array with 5.2 mu intersite spacing. Each site of the array is labeled from 1 to 16. The dashed arrows indicate the path of scanning. (b) The recorded values of error per gate as a function of site number. (Image by WIPM)




Scientists Realize High-Fidelity Single-Qubit Gates on Neutral Atoms---Chinese Academy of Sciences

Cheng Sheng, Xiaodong He, Peng Xu, Ruijun Guo, Kunpeng Wang, Zongyuan Xiong, Min Liu, Jin Wang, Mingsheng Zhan. High-Fidelity Single-Qubit Gates on Neutral Atoms in a Two-Dimensional Magic-Intensity Optical Dipole Trap Array. Phys. Rev. Lett. (2018). DOI: 10.1103/PhysRevLett.121.240501​

 

[JSCh]

PUBLIC RELEASE: 21-DEC-2018
Quantum tricks to unveil the secrets of topological materials
'Topological materials' are very interesting for technology, but difficult to study; TU Wien and the University of Science and Technology in China are presenting new approaches

VIENNA UNIVERSITY OF TECHNOLOGY

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Optical instruments at TU Wien. CREDIT: TU Wien

Electrons are not just little spheres, bouncing through a material like a rubber ball. The laws of quantum physics tell us that electrons behave like waves. In some materials, these electron waves can take on rather complicated shapes. The so-called "topological materials" produce electron states that can be very interesting for technical applications, but it is extremely difficult to identify these materials and their associated electronic states.

TU Wien (Vienna) and several research groups from China have now developed new ideas and implemented them in an experiment. A "crystal " made of light waves is created to hold atoms in a very special geometric pattern. These "light crystals", which have been used in different ways for the manipulation of atoms, can now be used to deliberately drive the system out of equilibrium. By switching between simple and complicated states, the system reveals whether or not it has topologically interesting states. These findings have now been published in the journal Physical Review Letters.

Bread Rolls and Donuts
The importance of topology can easily be seen if we pack too many things into a shopping bag: a bread roll may be slightly crushed and squeezed into a shape similar to a banana. Bread rolls and bananas have the same basic geometric structure, topologically they are the same. On the other hand, a donut has a hole in the middle - its topology is different. Even if it is slightly squeezed, its shape can still be easily distinguished from that of the bread roll.

"It is similar with quantum states," explains Prof. Jörg Schmiedmayer from Vienna Center for Quantum Science and Technology (VCQ) at TU Wien. "Quantum states can have a nontrivial topology which protects them with respect to certain perturbations. That's what makes them so interesting for technology, because you always have to deal with perturbations in every experiment and in every real world technological application." In 2016, the Nobel Prize in Physics for research was awarded for research on topological states of matter, but it is still considered extremely difficult to determine whether or not a certain material allows topologically interesting quantum states.

"Quantum states that are not in equilibrium, are changing rapidly," says Jörg Schmiedmayer. "This dynamics is notoriously difficult to understand, but as we have shown, it is a great way to obtain extremely interesting information about the system." Schmiedmayer cooperated with research teams from China. "The experiment was led by Prof. Shuai Chen, in the research group of Prof. Jian-Wei Pan. Both were once collaborators in my group in Heidelberg, and ever since their return to China, we have been work closely together," says Schmiedmayer. The TU Vienna and the Chinese University of Science and Technology (USTC, Heifei, China) signed a cooperation agreement in 2016, which strengthened research cooperation, especially in the field of physics.

An Imbalance Revealing Material Properties
With the help of interfering light waves, atoms can be held in pre-defined places, creating a regular grid of atoms, similar to a crystal, the atoms taking the roles of the electrons in a solid state crystal. By changing the light, the geometry of the atomic arrangement can be switched, in order to examine how the electron states would behave in a real solid state material.

"With this change, a massive imbalance is suddenly being generated," says Jörg Schmiedmayer. "The quantum states must rearrange and approach a new equilibrium, much like balls rolling down a hill until they find equilibrium in the valley. And during this process we can see clear signatures that tell us whether topologically interesting states are to be found or not. "

This is an important new insight for research on topological materials. One could even adapt the artificial light crystals to simulate certain crystal structures and in order to find new topological materials.



Quantum tricks to unveil the secrets of topological materials | EurekAlert! Science News

Wei Sun, Chang-Rui Yi, Bao-Zong Wang, Wei-Wei Zhang, Barry C. Sanders, Xiao-Tian Xu, Zong-Yao Wang, Joerg Schmiedmayer, Youjin Deng, Xiong-Jun Liu, Shuai Chen, Jian-Wei Pan. Uncover Topology by Quantum Quench Dynamics. Phys. Rev. Lett. (2018). DOI: 10.1103/physrevlett.121.250403​

 

[JSCh]

PUBLIC RELEASE: 11-JAN-2019
Arbitrary quantum channel simulation for a superconducting qubit
SCIENCE CHINA PRESS

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The schematic of the quantum channel simulation based on superconducting quantum system. CREDIT: ©Science China Press

The open quantum system and its control laid the foundation of quantum mechanical and quantum information theory. Due to the interaction with the environment, the evolution of practical quantum system should be described by a quantum channel, instead of a unitary evolution for a closed quantum system. The experimental studies on the quantum channel will not only deepen our understanding of the quantum open system, but also improve our ability to control the evolution of a quantum system, which is beneficial for the researches on quantum information and quantum computation. Therefore, the realization of arbitrary operation on a quantum bit, i.e. the simulation of an arbitrary quantum channel, is of great significance.

Recently, a research team lead by Luyan Sun from Tsinghua University collaborates with Chang-Ling Zou from University of Science and Technology of China, realized the arbitrary quantum channel simulation for a single qubit in a superconducting quantum circuit, and realized the arbitrary operation on a quantum bit. The experiments are based on a three-dimensional microwave cavity and a coupled superconducting transmon qubit, with the cavity serving as the target qubit and transmon serving as an ancillary qubit, the arbitrary repetitive quantum channel simulation on the photonic qubit is realized. It is worth mentioning that, they developed a novel experimental scheme to realize the open quantum system control, with only minimum quantum resources of a single ancillary qubit and the real-time quantum feedback technology. Such a scheme can also be generalized to a higher dimension to realize arbitrary qudit channel simulation, which still only requires only single ancillary qubit. The demonstrated quantum channel simulation can deterministically simulate the quantum bit evolution in an arbitrary physical environment and generated arbitrary quantum mixed state, would play an important role in the future applications, including quantum computation and quantum simulation.

###​

This work is supported by the National Key Research and Development Program of China (2017YFA0304303), National Natural Science Foundation of China (11474177), and Anhui Initiative in Quantum Information Technologies (AHY130000).

For more details, see:

Ling Hu, Xianghao Mu, Weizhou Cai, Yuwei Ma, Yuan Xu, Haiyan Wang, Yipu Song, Chang-Ling Zou, Luyan Sun. Experimental repetitive quantum channel simulation, Science Bulletin, 2018, 63(23):1551-1557, doi: 10.1016/j.scib.2018.11.010

https://www.sciencedirect.com/science/article/pii/S2095927318305292
​

Arbitrary quantum channel simulation for a superconducting qubit | EurekAlert! Science News

 

[JSCh]

RESEARCH ARTICLE | PHYSICS
Quantum generative adversarial learning in a superconducting quantum circuit

1. Ling Hu1,*,
2. Shu-Hao Wu2,*,
3. Weizhou Cai1,
4. Yuwei Ma1,
5. Xianghao Mu1,
6. Yuan Xu1,
7. Haiyan Wang1,
8. Yipu Song1,
9. Dong-Ling Deng1,†,
10. Chang-Ling Zou2,† and
11. Luyan Sun1,†

See all authors and affiliations

Science Advances 25 Jan 2019:
Vol. 5, no. 1, eaav2761
DOI: 10.1126/sciadv.aav2761

Abstract
Generative adversarial learning is one of the most exciting recent breakthroughs in machine learning. It has shown splendid performance in a variety of challenging tasks such as image and video generation. More recently, a quantum version of generative adversarial learning has been theoretically proposed and shown to have the potential of exhibiting an exponential advantage over its classical counterpart. Here, we report the first proof-of-principle experimental demonstration of quantum generative adversarial learning in a superconducting quantum circuit. We demonstrate that, after several rounds of adversarial learning, a quantum-state generator can be trained to replicate the statistics of the quantum data output from a quantum channel simulator, with a high fidelity (98.8% on average) so that the discriminator cannot distinguish between the true and the generated data. Our results pave the way for experimentally exploring the intriguing long-sought-after quantum advantages in machine learning tasks with noisy intermediate–scale quantum devices.​

Quantum generative adversarial learning in a superconducting quantum circuit | Science Advances

 

[JSCh]

Researchers Realize Solid-state Programmable Quantum Processor Under Ambient Conditions
Jan 31, 2019

A research team led by Prof. DU Jiangfeng at the University of Science and Technology of China (USTC) of Chinese Academy of Sciences (CAS) realized the first solid-state programmable quantum processor under room temperature. This study was published in npj Quantum Information.

Quantum computer is a promising technique that utilizes the superposition and entanglement of physical states. In most of the quantum computing experiments, their systems are only designed to run specific quantum algorithms. To solve this problem, the concept of programmable quantum computing is proposed. Instead of altering the hardware, this method enables the quantum processor to perform any given tasks by simply reconfiguring relative parameters.

In recent years, programmable quantum computation has been demonstrated using trapped ions, superconducting qubits and quantum-dot-based qubits. Nonetheless, considering the vulnerability of quantum coherence to noises, it remains a challenge to construct a solid-state programmable quantum processor under room temperature.

With the electronic spin and 14N nuclear spin of nitrogen-vacancy (NV) center in diamond acting as a two-qubit system, researchers were able to form a programmable quantum processor that can perform quantum algorithms under room temperature. They used green laser pulses to realize the initialization and readout of the quantum processor.

Meanwhile, taking advantage of the designed universal quantum circuit, researchers transformed the execution of a series of quantum algorithms into the corresponding amplitudes and phases of microwave and radio frequency pulses. Up to this point, running a variety of quantum algorithms without tedious and expensive hardware reconfiguration are allowed through effective configuration of relative parameters.

In the course of quantum algorithm executing process, researchers incorporated the previous developed dynamic decoupling technology, effectively suppressing the adverse effects of noises in solids. They implemented Deutsch-Jozsa and Grover search algorithms on the programmable quantum processor with average success rates above 80%.

In the future, a further increase of the quantum algorithm success rates is expected via improving the material (diamond) performance of the quantum processor (e.g. reducing the abundance of 13C isotope).

This study demonstrated the flexibility of programmable quantum processors, taking an important step on the construction of a room-temperature solid-state quantum computing system.


Researchers Realize Solid-state Programmable Quantum Processor Under Ambient Conditions---Chinese Academy of Sciences

 

[JSCh]

RESEARCH ARTICLE | PHYSICS
Quantum generative adversarial learning in a superconducting quantum circuit

1. Ling Hu1,*,
2. Shu-Hao Wu2,*,
3. Weizhou Cai1,
4. Yuwei Ma1,
5. Xianghao Mu1,
6. Yuan Xu1,
7. Haiyan Wang1,
8. Yipu Song1,
9. Dong-Ling Deng1,†,
10. Chang-Ling Zou2,† and
11. Luyan Sun1,†

See all authors and affiliations

Science Advances 25 Jan 2019:
Vol. 5, no. 1, eaav2761
DOI: 10.1126/sciadv.aav2761

Abstract
Generative adversarial learning is one of the most exciting recent breakthroughs in machine learning. It has shown splendid performance in a variety of challenging tasks such as image and video generation. More recently, a quantum version of generative adversarial learning has been theoretically proposed and shown to have the potential of exhibiting an exponential advantage over its classical counterpart. Here, we report the first proof-of-principle experimental demonstration of quantum generative adversarial learning in a superconducting quantum circuit. We demonstrate that, after several rounds of adversarial learning, a quantum-state generator can be trained to replicate the statistics of the quantum data output from a quantum channel simulator, with a high fidelity (98.8% on average) so that the discriminator cannot distinguish between the true and the generated data. Our results pave the way for experimentally exploring the intriguing long-sought-after quantum advantages in machine learning tasks with noisy intermediate–scale quantum devices.​

Quantum generative adversarial learning in a superconducting quantum circuit | Science Advances

Tsinghua University Proves Quantum Supremacy on GANs
Synced
Jan 31

Many scientists believe that a quantum computing device will one day perform highly complex computational tasks which are far beyond the ability of today’s classical computers.

This theory is known as Quantum Supremacy, and scientists are engaged in various research efforts to advance it. A recent publication has created quite a buzz in the quantum community: A Tsinghua University research paper has for the first time reported an experimental demonstration of quantum generative adversarial learning in a superconducting quantum circuit. The trained quantum network, QGAN, achieved an impressive 98.8 percent average accuracy in generating quantum data that is indistinguishable from real data.

The paper Quantum Generative Adversarial Learning In A Superconducting Quantum Circuit was first submitted to ArXiv last August, and has now been published in the respected multidisciplinary open-access scientific journal Science Advances.


Click to continue reading -->

 

[JSCh]

28 February 2019
Researchers Move Closer to Practical Photonic Quantum Computing
New method fills critical need to measure large-scale quantum correlation of single photons

WASHINGTON — For the first time, researchers have demonstrated a way to map and measure large-scale photonic quantum correlation with single-photon sensitivity. The ability to measure thousands of instances of quantum correlation is critical for making photon-based quantum computing practical.

Caption: Xian-Min Jin, from Shanghai Jiao Tong University, leads the research team that developed a new approach for mapping and measuring photonic correlation with direct single-photon imaging. The new approach could also be useful for quantum simulation, quantum communication, quantum sensing and single-photon biomedical imaging.
Credit: Xian-Min Jin, Shanghai Jiao Tong University

In Optica, The Optical Society's journal for high impact research, a multi-institutional group of researchers reports the new measurement technique, which is called correlation on spatially-mapped photon-level image (COSPLI). They also developed a way to detect signals from single photons and their correlations in tens of millions of images.

“COSPLI has the potential to become a versatile solution for performing quantum particle measurements in large-scale photonic quantum computers,” said the research team leader Xian-Min Shanghai Jiao Tong University, China. “This unique approach would also be useful for quantum simulation, quantum communication, quantum sensing and single-photon biomedical imaging.”

Interacting photons

Quantum computing technology promises to be significantly faster than traditional computing, which reads and writes data encoded as bits that are either a zero or one. Instead of bits, quantum computing uses qubits that can be in two states at the same time and will interact, or correlate, with each other. These qubits, which can be an electron or photon, allow many processes to be performed simultaneously.

One important challenge in the development of quantum computers is finding a way to measure and manipulate the thousands of qubits needed to process extremely large data sets. For photon-based methods, the number of qubits can be increased without using more photons by increasing the number of modes encoded in photonic degrees of freedom— such as polarization, frequency, time and location — measured for each photon. This allows each photon to exhibit more than two modes, or states, simultaneously. The researchers previously used this approach to fabricate the world’s largest photonic quantum chips, which could possess a state space equivalent to thousands of qubits.

However, incorporating the new photonic quantum chips into a quantum computer requires measuring all the modes and their photonic correlations at a single-photon level. Until now, the only way to accomplish this would be to use one single-photon detector for each mode exhibited by each photon. This would require thousands of single-photon detectors and cost around 12 million dollars for a single computer.

“It is economically unfeasible and technically challenging to address thousands of modes simultaneously with single-photon detectors,” said Jin. “This problem represents a decisive bottleneck to realizing a large-scale photonic quantum computer.”

Single-photon sensitivity

Although commercially available CCD cameras are sensitive to single photons and much cheaper than single-photon detectors, the signals from individual photons are often obscured by large amounts of noise. After two years of work, the researchers developed methods for suppressing the noise so that single photons could be detected with each pixel of a CCD camera.

Caption: This illustration represents a new approach for mapping and measuring photonic correlation with direct single-photon imaging called correlation on spatially-mapped photon-level image (COSPLI). This innovative and powerful tool could help boost quantum information processing.
Credit: Xian-Min Jin, Shanghai Jiao Tong University

The other challenge was to determine a single photon’s polarization, frequency, time and location, each of which requires a different measurement technique. With COSPLI, the photonic correlations from other modes are all mapped onto the spatial mode, which allows correlations of all the modes to be measured with the CCD camera.

To demonstrate COSPLI, the researchers used their approach to measure the joint spectra of correlated photons in ten million image frames. The reconstructed spectra agreed well with theoretical calculations, thus demonstrating the reliability of the measurement and mapping method as well as the single-photon detection. The researchers are now working to improve the imaging speed of the system from tens to millions of frames per second.

“We know it is very hard to build a practical quantum computer, and it isn’t clear yet which implementation will be the best,” said Jin. “This work adds confidence that a quantum computer based on photons may be a practical route forward.”

Paper: K. Sun, J. Gao, M.-M. Cao, Z.-Q. Jiao, Y. Liu, Z.-M. Li, E. Poem, A. Eckstein, R.-J. Ren, X.-L. Pang, H. Tang, I. A. Walmsley, X.-M. Jin, “Mapping and Measuring Large-scale Photonic Correlation with Single-photon Imaging,” Optica, 6, 3, 244-249 (2019).
DOI: https://doi.org/10.1364/OPTICA.6.000244



Researchers Move Closer to Practical Photonic Quantum Computing | News Releases | The Optical Society

 

[JSCh]

Genuine 12-Qubit Entanglement on a Superconducting Quantum Processor
Ming Gong, Ming-Cheng Chen, Yarui Zheng, Shiyu Wang, Chen Zha, Hui Deng, Zhiguang Yan, Hao Rong, Yulin Wu, Shaowei Li, Fusheng Chen, Youwei Zhao, Futian Liang, Jin Lin, Yu Xu, Cheng Guo, Lihua Sun, Anthony D. Castellano, Haohua Wang, Chengzhi Peng, Chao-Yang Lu, Xiaobo Zhu, and Jian-Wei Pan

Phys. Rev. Lett. 122, 110501 – Published 20 March 2019

ABSTRACT
We report the preparation and verification of a genuine 12-qubit entanglement in a superconducting processor. The processor that we designed and fabricated has qubits lying on a 1D chain with relaxation times ranging from 29.6 to 54.6  μs. The fidelity of the 12-qubit entanglement was measured to be above 0.5544±0.0025, exceeding the genuine multipartite entanglement threshold by 21 statistical standard deviations. After thermal cycling, the 12-qubit state fidelity was further improved to be above 0.707±0.008. Our entangling circuit to generate linear cluster states is depth invariant in the number of qubits and uses single- and double-qubit gates instead of collective interactions. Our results are a substantial step towards large-scale random circuit sampling and scalable measurement-based quantum computing.​

Received 6 November 2018
DOI:https://doi.org/10.1103/PhysRevLett.122.110501
© 2019 American Physical Society


Phys. Rev. Lett. 122, 110501 (2019) - Genuine 12-Qubit Entanglement on a Superconducting Quantum Processor

 

[Menthol]

I heard that China and USA qubit are different.

China is only 12 while I heard USA is already aim for 128, if I'm not mistake.

I wonder what is the difference? Why is China so slow?

 

[JSCh]

PUBLIC RELEASE: 21-MAR-2019
Semiconductor: A new contender for scalable quantum computing
SCIENCE CHINA PRESS

Semiconductor quantum devices. A: A scanning eletron microscope of the semiconductor quantum device containing two charge qubits. B: A three-dimensional model of a design for scalable fault tolerant quantum computing based on spin qubits in semiconductor quantum dots.
©Science China Press

Quantum computing, along with 5G and AI, has been the focus for the next-generation technology in the last decades. Up to now, numerous physical systems have been investigated to build a test device for quantum computing, including superconducting Josephson junctions, trapped ions and semiconductors. Among them, the semiconductors is a new star for its high control fidelity and promise for integration with classical CMOS technology. Professor Guo-Ping Guo with his co-workers, Xin Zhang and Hai-Ou Li from the Key Laboratory of Quantum Information, Chinese Academy of Sciences, University of Science and Technology of China, reviewed recent developments of qubits based on semiconductors and discussed the challenges and opportunities for scalable quantum computing. This work, entitled "Semiconductor quantum computation" was published in National Science Review (Natl Sci Rev 2019; 6: 32-54).

Qubit, or quantum bit, like the bit in a classical computer, is the basic unit of a quantum processor. According to the life cycle of a qubit technology, the typical qubit progression can be roughly divided into six stages. It starts from the demonstration of single- and two-qubit control and measurement of coherence time (Stage I), then moves to the benchmarking of control and readout fidelity of three to ten qubits (Stage II). With these developments, the demonstration of certain error correction of some physical qubits can be made (Stage III) and after that, a logical qubit made from error correction of physical qubits (Stage IV) and corresponding complex control should be completed (Stage V). Finally, a scalable quantum computer composed of such logical qubits is built for fault tolerant computing (Stage VI). In the fields of semiconductor quantum computing, there are various types of qubits spanning from spin qubits, charge qubits, singlet-triplet qubits, exchange-only qubits, hybrid qubits and etc. Among them, control of both single- and two-qubit gates were demonstrated for spin qubits, charge qubits and singlet-triplet qubits, which suggests they have finished stage I and the on-going researches shows the state II is also going to be completed. Up to now, benchmarking of single- and two-qubit control fidelity near the fault tolerant threshold were demonstrated and scaling up to three or more qubits are necessary in the following years. One example of such devices is shown in figure (a), which was fabricated by Guo guoping's group at the University of Science and Technology of China for coherently controlling the interaction between two charge qubit states.

For further developments, there are still some challenges to resolve. In this review, the authors put forward three major problems as more effective and reliable readout methods, uniform and stable materials, and scalable designs. Approaches to overcome these obstacles have been investigated by a number of groups, such as employing microwave photons to detect charge or spin states and using purified silicon to replace gallium arsenide for spin control. The scalable designs with the strategy for wiring readout lines and control lines were also proposed, and in these plans the geometry and operation time constraints, engineering configuration for the quantum-classical interface, suitability for different fault tolerant codes to implement logical qubits were also discussed. One example of such design is illustrated in figure (B), which was proposed by Li et al. at Delft University of Technology in 2018. In such a device, the crossbar architecture of electrodes can form an array of electrons in silicon and their spin states can be controlled by microwave bursts.

In the light of arguments for noisy intermediate-scale quantum technology (NISQ), which means that a quantum computer with 50-100 qubits and low circuit depth that can surpass the capabilities of today's classical computers will be available in the near future, the authors anticipated that as a new candidate to compete in the field of scalable quantum computing with superconducting circuits and trapped ions, semiconductor quantum devices can also reach this technical level in the following years.



Semiconductor: A new contender for scalable quantum computing | EurekAlert! Science News

 

[JSCh]

Physics - Synopsis: Entangled Photon Source Ticks All Boxes
March 22, 2019
A quantum-dot-based device combines all of the attributes necessary for producing a reliable source of entangled photons for quantum information applications.

C.-Y. Lu/ University of Science and Technology of China​

Quantum photonic technologies require sources that create entangled, indistinguishable pairs of photons on demand that can be extracted from the source at a high rate. Previous experiments have achieved each of these four criteria individually, or in some combination, but have fallen short of fulfilling them all. For example, the method of creating entangled pairs by splitting a single high-energy photon into two—so-called spontaneous parametric down-conversion—lacks the capability to generate such photons on demand. Now, Hui Wang at the University of Science and Technology of China and colleagues demonstrate a semiconductor quantum-dot photon emitter that simultaneously achieves all the requirements in a single device.

The team illuminated an InGaAs quantum dot with a laser, producing an excited state made from two electron-hole pairs. When this state decayed back to the ground state, it yielded a pair of indistinguishable, entangled photons. The dot was embedded in the center of a circular grating, which functioned as a resonant cavity, enhancing photon emission and directing the entangled photons toward a lens, where they were collected. Using this scheme, the team avoided the disadvantage of other quantum-dot sources, which typically have poor photon extraction efficiency, as most of the photons generated by the dots are lost into the device.

The experiment’s performance is no record breaker by any individual measure. But this device is the first “all-rounder” and, as such, the team says, represents a significant milestone for quantum photonic applications. By refining the setup, the researchers hope to improve its capability on all four fronts, allowing for its eventual use in technologies such as quantum communication networks and optical quantum computers.

This research is published in Physical Review Letters.


–Marric Stephens
Marric Stephens is a freelance science writer based in Bristol, UK.

On-Demand Semiconductor Source of Entangled Photons Which Simultaneously Has High Fidelity, Efficiency, and Indistinguishability
Hui Wang, Hai Hu, T.-H. Chung, Jian Qin, Xiaoxia Yang, J.-P. Li, R.-Z. Liu, H.-S. Zhong, Y.-M. He, Xing Ding, Y.-H. Deng, Qing Dai, Y.-H. Huo, Sven Höfling, Chao-Yang Lu, and Jian-Wei Pan

Phys. Rev. Lett. 122, 113602 (2019)

Published March 22, 2019​

 

[JSCh]

OT.

The following article has nothing to do with China. It is a list of challenges that is facing quantum computing written by Intel's director of quantum hardware.

An Optimist’s View of the 4 Challenges to Quantum Computing - IEEE Spectrum
The technical challenges are very difficult, but the promise is too great to quit so early in the quantum computing marathon, writes Intel's Jim Clarke

By Jim Clarke

Photo: Intel
Intel's 17-superconducting-qubit test chip has already been superseded by a 49-qubit device.
This is a guest post. The views expressed in this article are solely those of the writer and do not represent positions of IEEE Spectrum, or the IEEE.

Quantum computers promise an exponential increase in power compared with today’s classical CMOS-based systems. This increase is of a magnitude that is difficult for the human mind to comprehend. So there is real excitement that quantum computers will deliver benefits that are not possible with today’s systems. With such promise, we are seeing the rise of quantum computing prophets who say that, in just a few years, these machines will have the ability change the world. And conversely, we’re seeing more quantum computing skeptics who say it will never happen.

At Intel, we are taking a pragmatic view of quantum computing. Our enterprise and high-performance computing customers are already asking for this capability from us. And we expect that demand to grow. However, quantum computing is still most certainly in the research stage. It may never work.

But we all see the enormous opportunities and they are worth pursuing.

Recently, a perspective published in IEEE Spectrum suggested that quantum computing will never materialize. Its main argument was that quantum computing will require control over an exponentially large number of quantum states, and that this amount of control is too difficult to achieve.

As both a quantum computing optimist and as a realist who has seen how long it takes for new semiconductor technologies to come to market, I recognize where the concern is coming from, but I believe it is still far too soon to say we’ll “never” realize the promise of quantum computing.

I believe there are four key challenges that could keep quantum computing from becoming a reality. But if solved, we could create a commercially relevant quantum computer in about 10-12 years, a computer that might change your life or mine.

1. Qubit Quality: We need to make qubits that we will be able to generate useful instructions or gate operations for on a large scale. As a community, we are not there yet. Even the few qubits in today’s cloud-based quantum computers are not good enough for large scale systems. They still generate errors when running operations between two qubits at a rate that is far higher than what we would need to effectively compute. In other words, after a certain number of instructions or operations, today’s qubits produce the wrong answer when we run calculations. The result we get can be indistinguishable from noise.
2. Error Correction: Now, because qubits aren’t quite good enough for the scale we need them to operate at, we need to implement error correction algorithms that check and then correct for random qubit errors as they occur. These are complex instruction sets that use many physical qubits to effectively extend the lifetime of the information in the system. Error correction has not yet been proven at scale for quantum computing, but it is a priority area of our research and one that I consider a prerequisite to a full-scale commercial quantum system.
3. Qubit Control: In order to implement complex algorithms, including error correction schemes, we need to prove that we can control multiple qubits. That control must have low-latency—on the order of 10’s of nanoseconds. And it must come from CMOS-based adaptive feedback control circuits. This is a similar argument to that made in the aforementioned IEEE Spectrum article. However, though it is daunting, I have every reason to believe it is not impossible.
4. Too Many Wires: Finally, we need to address “fan-out”—or how to scale up the number of qubits within a quantum chip. Today, we require multiple control wires, or multiple lasers, to create each qubit. It is difficult to believe that we could build a million-qubit chip with many millions of wires connecting to the circuit board or coming out of the cryogenic measurement chamber. In fact, the semiconductor industry recognized this problem in the mid-1960s and designated it Rent’s Rule. Put another way, we will never drive on the quantum highway without well designed roads.

At Intel, we are working to tackle each of these challenges. As an example, we are working on qubits that operate at slightly higher temperatures and would, therefore, allow co-integration with CMOS-based electronics to facilitate qubit control. Higher temperature allows us to put CMOS electronics into the fridge without impacting the quantum states. Local CMOS electronics help us with the latency of our control systems and allow for more freedom for qubit wiring or interconnects.

It will take work. Do not be fooled by shiny tools or by pronouncements that this technology will arrive tomorrow. Every major change in the semiconductor community has happened on the decade timescale: from the transistor in 1947 to the integrated circuit in 1958 to the first microprocessor, the Intel 4004, in 1970. At the same time, do not be defeated by pronouncements of “never.”

The potential is too great, and the stakes are too high to quit at mile one of a marathon.

About the Author: Jim Clarke is director of quantum hardware at Intel.

 

[Han Patriot]

I heard that China and USA qubit are different.

China is only 12 while I heard USA is already aim for 128, if I'm not mistake.

I wonder what is the difference? Why is China so slow?

I heard Indians did zero qubits. What happened to you vedic geniuses?

 

[antonius123]

I heard Indians did zero qubits. What happened to you vedic geniuses?

He is not Indian. He is asking genuine question.

 

[JSCh]

Optical toric code platform sets new record
March 26, 2019, University of Science and Technology of China

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The experimental setup. Ultraviolet laser pulses with a central wave-length of 394 nm, pulse duration of 150 fs, and repetition rate of 80 MHz pass through three HWP-sandwiched BBO crystals and a single BBO to produce three entangled photon pairs (in spatial modes 1-3, 5-6, and 7-9) and a pair of photons (in spatial 4-8), respectively. All of these photons are put into a linear optical net- work to prepare the ground state. The steps of ground state preparation, anyon creation, anyon braiding, anyon annihilation, and measurement are marked.(C-BBO, sandwich-like BBO + HWP + BBO combination; S-BBO, single BBO; QWP, quarter-wave plate; HWP, half-wave plate; PBS, polarizing beam splitter; D-PBS, double PBS; D-BS, double beam splitter.) Credit: LIU Chang

Anyons form the basis for topological quantum computation and error correction, where the topological aspect of anyonic braiding is one of the important features that gives rise to fault tolerance. More qubits to control will assist researchers to explore further.

Recently, a research group led by professor Pan Jianwei and Lu Chaoyang of University of Science and Technology of China successfully designed the largest planar code platform at present using photons, and demonstrated path-independent property in optical system for the first time.

The group first generated the 8 entanglement photons using spontaneous parametric down-conversion and interference. One of the photons is encoded with polarization and path, eventually creating the 9 qubits anyons models.

Then, researchers performed braiding operations on the anyons. Thanks to more qubits, the platform contains enough lattices for demonstration of path-independent property. If two operations have topologically equivalent paths, phase offset of system will remain unchanged. By measuring this offset, path-independent property was observed in the system.

This work provides a platform for simulating the braiding operations with linear optics. Researchers are able to conduct more complicated experiments on the features of anyonic statistics in the future.

The result was published on Optica.

More information: Chang Liu et al, Demonstration of topologically path-independent anyonic braiding in a nine-qubit planar code, Optica (2019). DOI: 10.1364/OPTICA.6.000264



Read more at: https://phys.org/news/2019-03-optical-toric-code-platform.html