Jul 8, 1985 David Deutsch describes a universal quantum computer

In 1981 Richard Feynman had argued that only a computer built on quantum principles could efficiently simulate nature. Four years later David Deutsch, a physicist at Oxford, gave the idea a precise form. He described a universal quantum computer: a device that, like the universal Turing machine on which ordinary computing rests, could run any program, but whose memory obeyed the laws of quantum mechanics.

Such a machine, he showed, could simulate any physical system governed by those laws, and through what he called "quantum parallelism" it could carry out certain tasks faster than any classical computer. It existed only on paper. Nobody knew how to build one, or what it would be good for.

Computing machines resembling the universal quantum computer could, in principle, be built and would have many remarkable properties not reproducible by any Turing machine. These do not include the computation of non-recursive functions, but they do include ‘quantum parallelism’, a method by which certain probabilistic tasks can be performed faster by a universal quantum computer than by any classical restriction of it.

Dec 18, 1995 NIST team demonstrates a quantum logic gate with a single trapped ion

Deutsch had described what a quantum computer would be; the decade that followed showed what one might do. Researchers found the first problems on which it would outpace conventional machines, and in 1994 Peter Shor showed that it could factor large numbers efficiently, enough to break much of the encryption that secures the internet. Yet not even the smallest component of such a device had been built.

Like any other computer, a quantum one would be assembled from logic gates, and a particular kind is indispensable: the controlled-NOT, in which the state of one qubit decides whether another flips. The difficulty is performing it without disturbing either of them, since even slight contact with the surroundings destroys a quantum state.

In May 1995 Ignacio Cirac and Peter Zoller proposed a method: trap charged atoms, or ions, in a vacuum, cool them nearly to rest, and manipulate them with laser light. Seven months later a NIST group in Boulder, Colorado, led by Christopher Monroe and David Wineland, demonstrated a version of the scheme on a single beryllium ion. One qubit was stored in the ion's internal state, the other in its vibration within the trap, and a sequence of pulses performed the controlled-NOT between them.

Combined with simple operations on individual qubits, already within reach, the controlled-NOT suffices for any quantum computation. The experiment had therefore supplied the essential ingredient of the machine Deutsch had described, and every quantum processor built since rests on the same step. In 2012 Wineland shared the Nobel Prize in Physics; the committee credited his work with "the very first steps towards building a new type of super-fast computer, based on quantum physics."

We demonstrate the operation of a two-bit "controlled-NOT" quantum logic gate, which, in conjunction with simple single-bit operations, forms a universal quantum logic gate for quantum computation.

Jan 1998 First quantum algorithms run on small NMR quantum computers

The NIST gate was a single step. A computation chains many such steps into an algorithm, and by 1997 nobody had run one on quantum hardware. Trapped ions and atoms in optical cavities had produced individual gates, but not yet a complete calculation.

A different route came from chemistry. In 1996 and 1997 two groups independently proposed using the nuclei of atoms within ordinary molecules as qubits. Each nucleus behaves like a tiny compass needle: in a strong field it lines up with it or against it, and pulses of radio waves can turn it. This is nuclear magnetic resonance (NMR), the physics behind hospital MRI scanners. A sample of liquid holds an enormous number of identical molecules, each a copy of the same small computer, and the instrument reads their combined signal.

In January 1998 the first quantum algorithms ran on such machines. At Oxford, Jonathan Jones and Michele Mosca used cytosine, one of the bases of DNA; Isaac Chuang's team at IBM, Stanford and MIT used chloroform, about a billion billion molecules in half a millilitre. Each machine had two qubits. Both solved Deutsch's problem in its simplest form: a hidden function turns one bit into another, and the task is to decide whether it always gives the same output. A classical computer needs two evaluations of the function; the quantum algorithm needs one.

The problem is deliberately trivial; what mattered was that quantum hardware had run a program from start to finish and returned the correct answer. By May the Oxford group had also run Grover's search algorithm. NMR, however, had a limit that its own proponents pointed out: the molecules start out in nearly random orientations, and the usable signal shrinks exponentially as qubits are added. The method could not be scaled much beyond a handful of qubits.

We demonstrate the use of an NMR quantum computer based on the pyrimidine base cytosine, and the implementation of a quantum algorithm to solve Deutsch's problem.

Apr 29, 1999 NEC researchers control a superconducting qubit for the first time

NMR had shown what a quantum algorithm looked like in practice, but its qubits could not be multiplied at will. Ions and nuclei are supplied by nature; a large quantum computer would need components that could be manufactured, the way transistors are printed onto silicon.

One candidate was the superconducting circuit. Cooled to a fraction of a degree above absolute zero, certain metals carry current without resistance, and a small circuit made from them can behave as a single quantum object. The question was whether such a circuit could hold a superposition and be steered by electrical signals alone.

In April 1999 Yasunobu Nakamura and his colleagues at the Japanese electronics company NEC reported that it could. Their device, a "Cooper-pair box", was a tiny island of superconducting metal whose two states differed by a single pair of electrons. A short voltage pulse placed the island in a superposition of both, and a probe junction read out the result. It was the first qubit built not from an atom but from an electronic circuit.

The quantum state was extremely fragile, far too short-lived for useful computation. But the device was made with lithography, like an ordinary chip, and its descendants became the qubits of many of the quantum computers built since, including those of IBM and Google.

Here we report the observation of quantum oscillations in a single-Cooper-pair box. By applying a short voltage pulse via a gate electrode, we can control the coherent quantum state evolution: the pulse modifies the energies of the two charge states non-adiabatically, bringing them into resonance. The resulting state—a superposition of the two charge states—is detected by a tunnelling current through a probe junction. Our results demonstrate electrical coherent control of a qubit in a solid-state electronic device.

Feb 25, 2000 David DiVincenzo lists the requirements for building a quantum computer

By the end of the decade there were several ways to make a qubit: trapped ions, nuclei in molecules, superconducting circuits, and proposals based on single electrons in semiconductors. Each laboratory could report progress, but on its own terms, and the results were hard to compare. What, exactly, would a technology have to achieve to become a quantum computer?

In February 2000 David DiVincenzo, a physicist at IBM, set out an answer that became the field's common yardstick.

His requirements were five. The system must hold well-defined qubits and be able to grow to many of them. Every qubit must be set to a known starting state. The qubits must keep their quantum state far longer than an operation takes. There must be a universal set of gates, such as the controlled-NOT together with single-qubit operations. And each qubit must be readable at the end. Two further requirements concerned sending quantum information from one machine to another.

The list did not say which technology would win; it said what any of them would have to deliver. From then on, a claim to have built a quantum computer could be tested against it, point by point.

the requirements for the physical implementation of quantum computation are discussed. These five requirements, plus two relating to the communication of quantum information, are extensively explored

Dec 20, 2001 IBM and Stanford run Shor's algorithm on a 7-qubit computer to factor 15

Shor's algorithm was the main reason quantum computing had drawn so much attention, yet it had never been run. Even the smallest meaningful case requires several qubits working together through a long sequence of operations, well beyond the two-qubit machines of 1998.

At IBM's Almaden laboratory in California, Isaac Chuang's group, working with colleagues at Stanford, pushed NMR as far as it would go. They used a molecule synthesized for the purpose, in which seven atomic nuclei served as qubits, and controlled it with carefully timed radio-frequency pulses.

In December 2001 they reported in Nature that the molecule had found the prime factors of 15: 3 and 5. It was the simplest instance of Shor's algorithm, chosen so that a seven-qubit machine could manage it, and the answer was known in advance.

The result said nothing new about the number 15. What it showed was that the algorithm behaved on real hardware as Shor had predicted. It was also close to the ceiling of NMR, whose signal weakens with every qubit added: the method that ran the first quantum algorithms could not carry them much further.

Here we report an implementation of the simplest instance of Shor's algorithm: factorization of N = 15 (whose prime factors are 3 and 5). We use seven spin-1/2 nuclei in a molecule as quantum bits

Feb 13, 2007 D-Wave demonstrates Orion, which it calls the first commercial quantum computer

Through the early 2000s quantum computers remained laboratory experiments with a handful of qubits. Then, on February 13, 2007, a Canadian start-up called D-Wave Systems presented a machine it described as "the world's first commercial quantum computer."

The demonstration took place at the Computer History Museum in Mountain View, California. The machine, called Orion, had 16 qubits on a superconducting chip made of niobium, and on stage it solved problems such as a Sudoku puzzle.

Orion was not the kind of machine DiVincenzo had described. It did not run arbitrary sequences of gates; it was built for one kind of task, searching for the best solution to an optimization problem, using an approach known as quantum annealing.

D-Wave released few technical details and no peer-reviewed evidence that its results depended on quantum effects. Researchers such as Scott Aaronson and Umesh Vazirani called the claims misleading, noting that Orion showed no advantage over ordinary computers. The question of what counts as a quantum computer had acquired a commercial edge.

On February 13, D-Wave Systems, a startup based in Burnaby, British Columbia, claimed to have demonstrated "the world's first commercial quantum computer."

Jun 28, 2009 Yale researchers run quantum algorithms on a solid-state processor for the first time

While the debate over D-Wave continued, laboratories were improving the superconducting qubit that NEC had first demonstrated. The early devices lost their quantum state almost at once. In 2007 a group at Yale introduced the transmon, a design far less sensitive to stray electrical noise, which held its state much longer.

The next step was to put several such qubits on one chip, make them interact on command, and run an algorithm with them.

In June 2009 Leonardo DiCarlo, Robert Schoelkopf and their colleagues at Yale reported a chip with two transmon qubits, coupled through a microwave cavity that acted as a bus between them. It ran simple versions of Grover's search and the Deutsch–Jozsa algorithm.

These were the same small algorithms run with NMR eleven years earlier. The difference was the hardware: an electronic circuit, fabricated on a chip and controlled by microwave signals, like a rudimentary microprocessor. Yale described it as the first electronic quantum processor. It was the approach that IBM and Google would later scale up.

Here we demonstrate a two-qubit superconducting processor and the implementation of the Grover search and Deutsch–Jozsa quantum algorithms

May 2011 Lockheed Martin buys the D-Wave One, billed as the first commercial quantum computer

D-Wave, meanwhile, had kept building. In May 2011 it announced the first sale of what it called the world's first commercially available quantum computer: a D-Wave One, with 128 qubits, bought by the defense contractor Lockheed Martin for a reported $10 million.

Shortly before, D-Wave had published a paper in Nature presenting evidence that its chips relied on quantum effects.

Many independent researchers remained skeptical. The paper did not show that the machine solved any problem faster than a conventional computer, and it remained unclear how much of its behavior was quantum at all.

The sale, however, was a fact. For the first time a machine marketed as a quantum computer had been bought by a customer. It was installed at the University of Southern California, where Lockheed Martin and USC ran it together. What had changed hands was a special-purpose device of disputed nature; whether it deserved the name depended on what the term was taken to mean.

Eleven years ago, together with Lockheed Martin, we installed our first quantum system at USC.

May 4, 2016 IBM puts a five-qubit quantum computer online for the public

Until 2016 a quantum computer could be used only by the researchers who built it, in the laboratory where it stood. On May 4 that year IBM put one online.

Through a website called the IBM Quantum Experience, anyone could design a circuit and run it on a five-qubit superconducting processor at IBM's research center in Yorktown Heights, New York. IBM described it as the first time quantum computing had been made available to the public.

The processor was small, and the experiments it could run were short. But the barrier between the machine and its users had gone: students, programmers and researchers who had never entered a quantum laboratory could now program real hardware and see the results.

In March 2017 IBM released Qiskit, an open-source toolkit for writing such programs, and other companies followed with cloud services of their own. Access over the internet became the usual way to use a quantum computer.

IBM (NYSE: IBM) Research announced today that for the first time ever it is making quantum computing available to members of the public, who can access and run experiments on IBM's quantum processor.

Aug 3, 2016 Maryland researchers program a five-qubit trapped-ion computer

Most quantum experiments until then had been arranged for a single purpose: the pulses, their timing and the hardware were set up to run one particular algorithm, and running another meant reworking much of the setup.

In August 2016 a team at the University of Maryland led by Christopher Monroe, who had helped demonstrate the first quantum logic gate at NIST in 1995, reported a different approach.

Their machine held five trapped ions, each a qubit. Software translated an algorithm into a sequence of operations native to the hardware, so the same device could run different calculations without being altered. The team ran several: the Deutsch–Jozsa and Bernstein–Vazirani algorithms, and a quantum Fourier transform, the step at the heart of Shor's algorithm.

In the terms Deutsch had used in 1985, this was a machine that could be programmed rather than rebuilt. The paper's title called it a small programmable quantum computer.

five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms

Jan 8, 2019 IBM unveils Q System One, what it calls the first integrated quantum computing system

By 2019 quantum computers existed in several laboratories and companies, but they still looked like experiments: refrigerators, cables and electronics spread across a room and tuned by the people who had built them.

At the CES technology show in Las Vegas in January 2019, IBM presented a different object: the IBM Q System One, a quantum computer sealed together with its cooling and control electronics inside a glass case nine feet tall.

IBM called it the world's first integrated quantum computing system for commercial use, designed for stability, reliability and continuous operation outside the research lab. Customers could not buy one or see it at work, however: like the 2016 machine, it was reached only through IBM's cloud.

Between 1985 and 2019 the title of first quantum computer had been claimed, or could be claimed, for a logic gate, a test tube of molecules, a chip, a sale, a website, a programmable set of ions and a glass case. Which of them deserves it depends on what one means by a computer.

Designed by IBM scientists, systems engineers and industrial designers, IBM Q System One has a sophisticated, modular and compact design optimized for stability, reliability and continuous commercial use. For the first time ever, IBM Q System One enables universal approximate superconducting quantum computers to operate beyond the confines of the research lab.