Global Publications Output in Quantum Computing Research: A Scientometric Assessment during 2007-16

The paper maps quantum computing research on various publication and citation indicators, using data from Scopus database covering 10-year period 2007-16. Quantum computing research cumulated 4703 publications in 10 years, registered a slow 3.39% growth per annum, and averaged 14.30 citations per paper during the period. Top 10 countries dominate the field with 93.15% global publications share. The USA accounted for the highest 29.98% during the period. Australia tops in relative citation index (2.0). International collaboration has been a major driver of research in the subject; 14.10% to 62.64% of national level output of top 10 countries appeared as international collaborative publications. Computer Science is one of the most popular areas of research in quantum computing research. The study identifies top 30 most productive organizations and authors, top 20 journals reporting quantum computing research, and 124 highly cited papers with 100+ citations per paper.

and more powerful computers in future [5,6].
Quantum computers are billed as fifth generation computers with major potential to solve so many different problems that are too complex or even impossible for today's computers.However, quantum computing technologies are still in their infancy stage and it will take years before such technologies are likely to come up for use on commercial scale.The ongoing developments in quantum computing technologies are mainly limited to developed world countries like USA, U.K., Canada, Japan, China, and Australia, [7][8][9].Quantum computing being a booming area of research, it would be worthwhile to map quantum computing research with a view to provide a quantitative and qualitative description of the subject under study.

1-1-Literature Review
Octamine provides a quantitative description of patenting activity in quantum computing research covering the period 1994-2014.According to this report, patenting activity has followed a growth in three cycles.Despite developments picking in 2013, breakthroughs in quantum computing technologies are still far way [10].Scanlon, Tony, and Mishra [11] in their report analysed three areas of quantum computing patents: qubits, hardware, and applications of quantum computing.Projections are that by 2017, qubit technologies will see the most patent family publications, followed closely by quantum hardware patents, and applications of patents.The report maps emerging quantum companies, the academic world and their patenting activities [11].No other studies are available as yet in the body of literature on bibliometric studies covering quantitative and qualitative description of quantum computing research per se.However, a number of bibliometric studies do exist on computer science research in general [8][9][12][13][14][15][16][17][18][19] and its subfields such as artificial intelligence [18,20], cloud computing [19][20][21][22], cryptography [21,23], computational intelligence [22,24], granular computing [23,25], grid computing [24,26], parallel computing [25,27], pervasive and ubiquitous computing [26,28], and software engineering [27,29], etc. in particular.

2-Objectives
The study has been undertaken with the intent to map the global quantum computing research as indexed in Scopus international database during 2007-16.The study seeks to describe the subject in terms its growth rate, citation impact, international collaborative publications, research output by top 10 most productive countries; distribution of research by broad subject areas, the dynamics of research growth and decline across sub-areas of quantum computing over time; publication and citation profile of top 30 most productive research organizations and authors; main modes of communication, and the bibliometric profile of top 124 highly cited papers.

3-Methodology
The study retrieved and downloaded 10-year publications data on quantum computing research using Scopus database (http://www.scopus.com)covering the publication period 2007-16.For downloading data a search string was formulated.The term "quantum computing'' was used as the keyword and tagged it to "Keyword" and "Source Title" search fields.To limit the global research output to publication period '2007-16', the search string formulated as stated above was conjoined with date range search field using Boolean Operator 'AND'.In the subsequent round of searching, the final search output was refined by using "subject area tag", "country tag", "source title tag", "journal title name" and "affiliation tag", in order to get data/information on the distribution of global publications output by subject, collaborating countries, author-wise, organization-wise and journal-wise, etc.For citation data, citations to publications were collected from date of publication till 13 November 2017.

4-1-Top 10 Most Productive Countries in the World in Quantum Computing Research
The global research output in quantum computing field originated from nearly 90 countries during 2007-16.The distribution of global publications output by participating countries is skewed.Of the 90 participating countries, contributed 1-10 papers each, 29 countries 11-50 papers each, 11 countries 51-100 papers each, 10 countries 101-1000 papers each and 1 country 1001-5000 paper.Top 10 countries dominated quantum computing research with 93.15% global publication share during the period (Table 2).Individually their global publication share varied from 3.51% to 29.98%.The USA contributed the highest 29.98% share, followed by China (15.35%),U.K. (8.70%), etc. Italy and France positioned at bottom end of the tally contributed 3.51% to 3.81% global publications share.

4-3-Distribution of Research Output by Sub-Fields
The global publication output in quantum computing research is distributed across nine sub-fields as identified in Scopus database classification.Computer science is the most popular area of research in quantum research accounting for the highest global publications share (44.89%), followed by physics and astronomy (39.55%), engineering (29.0%), mathematics (21.90%), materials science (14.18%), chemistry (9.97%) and other sub-field from 2.66% to 5.44% during 2007-16.

4-4-Profile of Top 30 Global Organizations
A total of 1642 organizations published 4703 publications in quantum computing research with an average of 2.86 publications per organization.The distribution of publication output across participating organizations is highly skewed.Of the 1642 organizations, 1301 contributed 1-5 papers each, 190 organizations 6-10 papers each, 134 organizations 11-50 papers each, 13 organizations 51-100 papers each and 4 organizations 101-160 papers each.
The publication productivity of top 30 most productive organizations in quantum computing research across the world varied from 30 to 102 publications.Together they accounted for 28.53% (1342) publication share and 65.36% (43958) citation share of total publications output in 10 years during 2007-16.
The scientometric profile of these top 30 organizations is presented in Table 4

4-6-Medium of Research Communication
Of the global research output in quantum computing field, 60.05% (2824) appeared in journals, 29.11% (1369) in conference proceedings, 7.08% (333) in book series, 2.83% (133) as books and 0.77% (36) as trade publications and 0.67%(58) as books.Of The top 20 most productive journals which published 21 to 198 papers each, accounted for 33.44% share (947 papers) of total papers in journal medium in 10 years during 2007-16.The top most productive journals include: Journal of Physical Review A (with 198 papers), followed by Physical Review Letters (139 papers), New Journal of Physics (82 papers), Quantum Information Processing (60 papers), Computer Physics Communication (49 papers), etc. during 2007-16 (Table 6).

4-7-Highly Cited Papers
For this study, all such papers that received 100 or 100 plus citations per paper in 10 years since their publication during 2007-16 have been acknowledged as highly cited papers in quantum computing field.A total of 124 papers were identified as highly cited papers, which accounted for 2.64% share of the total world output (4703 papers) in the subject during the period.The distribution of highly cited papers across discrete citations frequencies is highly skewed. These 124 highly cited papers cumulated a total of 33046 citations, with an average of 266.50 citations per paper.
 Of the 124 highly cited papers, 42 were contributed by such individual organizations who pursued research in their standalone capacity (non-collaborative) and 82 by such other collaborating organizations who pursued research as a group of two or more organizations per paper (25 national collaborative and 57 as international collaborative organizations).
 Amongst highly cited papers, research participation by a country was the largest from USA (with 56 papers), followed by Canada (22 papers), Germany (18 papers), Australia (15 papers), U.K. (

5-Conclusion
The present study provides a quantitative and qualitative description of quantum computing research across the world during 2007-16.The study sourced data for the study from the Scopus, an international multi-disciplinary database.Quantum computing research across the world cumulated a total of 4703 publications, and registered a slow 3.39% growth during the period.The top 10 countries that dominate the world of quantum computing research include the USA, China, UK, Germany, Japan, India, Canada, Australia, Italy and France, with 93.15% global publications share.Quantum computing research averaged a high citation impact of 14.30 citations per paper on a 10-year citation window.Six of the top 10 most productive countries scored relative citation index above the group average of 1.33.Computer science is one of the most popular areas of study in quantum computing research, accounting for the highest subject share (44.89%), followed by physics & astronomy (39.55%), and others.The top 30 most productive organizations in quantum computing research are mainly from developed world countries, like the USA (12), Japan (4), China (3), Australia (3), the U.K. (2), Austria (2), Canada (2), and France (1).Their citation impact averaged between 34.14 and 103.31CPP on a 10-year window.Over 60% of global publications share in the subject appeared in journal literature, with top 20 journals accounting for 33.44% share of total output covered by journal medium.
Quantum computing research till recently 2016 has been intensely strong on quality, but not as much on quantity of research.That its body of literature is still too small and its growth too slow, alludes to a view that quantum computing research is still very much in its early stages of development.Even as quantum computing research efforts are global in scope, but leadership in the subject still rests with the USA.Of the top 30 research institutes in the subject across the world, as many as 12 are located in the USA, and the rest distributed in single digits across eight countries like the U.K, China, Singapore, Canada, Japan, Australia, Austria, and France.

The 10 -
year quantum computing research across the world cumulated to 4703 publications during 2007-16, and it registered 3.39% growth, up from 391 in 2007 to 509 publications in 2016.The 5-year global output in the subject registered 7.73% absolute growth, up from 2264 in 2007-11 to 2439 publications in 2012-16.The 10-year citation impact of quantum computing research averaged to 14.30 citations per publication (CPP) during 2007-16.The 5-year citation impact of research in the subject declined from 21.76 CPP during 2007-11 to 7.38 CPP during 2012-16 (Table

Figure 1 .
Figure 1.Publications and Citations Output in Quantum Computing Research Across the World.

Figure 2 .
Figure 2. Global Publications Share of Top Countries in Quantum Computing Research during 2007-2016.


Of the 124 highly cited papers, 83 were in citation range 101-200 citations per paper, 19 in the range 201-300 citations per paper, 9 in the range 301-500 citations per paper, 7 in the range 501-900 citations per paper, 5 in the range 1001-2000 citations per paper and 1 lone paper cumulated 2705 citations since its publication during 2007-16.

Table 6 . Top 20 Most Productive Journals in Quantum Computing Research during 2007-16.
University of California, Santa Barbara, USA, Princeton University, USA, Harvard University, USA, University of Berkeley, USA, Osterreichische Akademie Der Wissenshaften, Austria and Perimeter Institute of Theoretical Physics, Waterloo, Canada (5 papers each), University of Oxford, U.K. AND university OF Melbourne, Australia (4 papers each), MIT, USA, Tsinghua University, China, University of Innsbruck, Austria and University of Maryland, USA (3 papers), etc.  The authors accounting for the largest number of highly cited papers include: A.G.Fowler (4 papers), T.C. Ralph, A. Aspuru-Guzik and S.T. Flammia (3 papers each), E. Kashefi, O. Pfister, J.W. Pan, N.C.Menicucci and R. Blatt, etc. (2 papers each).Of the 124 highly cited papers, 105 were published as articles, 14 as review papers and 5 as conference papers.These124highly cited papers were published across 50 national and international journals.Twenty one (21) papers appeared in Physical Review Letters, 13 papers in Nature, 8 papers in Science, 6 papers in Nature Photonics, 5 papers each in Journal of American Chemical Society and Physical Review A, 4 papers each in Nature Communications, Proceedings of NAS of USA and Review of Modern Physics, 2 papers each in Chemical Society Reviews, IEEE Transaction on Systems, Man & Cybernetics.Part B, IEEE Transactions on Power Systems, Molecular Physics, Nature Physics, New Journal of Physics and SIAM Journal of Computing and paper each in 34 other journals.
papers), China (11 papers), Italy, Spain and France (7 papers each), Japan and Netherland (5 papers), Poland and Israel (4 papers each, Belgium, Denmark, Taiwan and Switzerland (3 papers each), India , Singapore and South Korea (2 papers), Brazil, Russia Federation and Sweden (1 paper each). The 124 highly cited papers involved the participation of 720 authors from 379 organizations. The research organizations accounting for the largest number of highly cited papers include: University of Waterloo, Canada (9 papers), National Institute of Standards and Technology, USA and Stanford University, USA (6 papers each),