Achieving Quantum Supremacy

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Achieving Quantum Supremacy
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The UCSB/Google Quantum AI group (Photo: Matt Perko / UCSB)

By Sonia Fernandez, UC Santa Barbara

Researchers in UC Santa Barbara/Google scientist John Martinis’ group have made good on their claim to quantum supremacy. Using 53 entangled quantum bits (“qubits”), their Sycamore computer has taken on — and solved — a problem considered intractable for classical computers.

“A computation that would take 10,000 years on a classical supercomputer took 200 seconds on our quantum computer,” said Brooks Foxen, a graduate student researcher in the Martinis Group. “It is likely that the classical simulation time, currently estimated at 10,000 years, will be reduced by improved classical hardware and algorithms, but, since we are currently 1.5 billion times faster, we feel comfortable laying claim to this achievement.”

The feat is outlined in a paper in the journal Nature.

The milestone comes after roughly two decades of quantum computing research conducted by Martinis and his group, from the development of a single superconducting qubit to systems including architectures of 72 and, with Sycamore, 54 qubits (one didn’t perform) that take advantage of the both awe-inspiring and bizarre properties of quantum mechanics.

“The algorithm was chosen to emphasize the strengths of the quantum computer by leveraging the natural dynamics of the device,” said Ben Chiaro, another graduate student researcher in the Martinis Group. That is, the researchers wanted to test the computer’s ability to hold and rapidly manipulate a vast amount of complex, unstructured data.

“We basically wanted to produce an entangled state involving all of our qubits as quickly as we can,” Foxen said, “and so we settled on a sequence of operations that produced a complicated superposition state that, when measured, returned output ("bitstring") with a probability determined by the specific sequence of operations used to prepare that particular superposition." The exercise, which was to verify that the circuit’s output correspond to the sequence used to prepare the state, sampled the quantum circuit a million times in just a few minutes, exploring all possibilities — before the system could lose its quantum coherence.

Google’s quantum supreme cryostat with Sycamore inside (Photo: Eric Lucero/Google)

‘A complex superposition state’ 

“We performed a fixed set of operations that entangles 53 qubits into a complex superposition state,” Chiaro explained. “This superposition state encodes the probability distribution. For the quantum computer, preparing this superposition state is accomplished by applying a sequence of tens of control pulses to each qubit in a matter of microseconds. We can prepare and then sample from this distribution by measuring the qubits a million times in 200 seconds.”

“For classical computers, it is much more difficult to compute the outcome of these operations because it requires computing the probability of being in any one of the 2^53 possible states, where the 53 comes from the number of qubits — the exponential scaling is why people are interested in quantum computing to begin with,” Foxen said. “This is done by matrix multiplication, which is expensive for classical computers as the matrices become large.”

According to the new paper, the researchers used a method called cross-entropy benchmarking to compare the quantum circuit’s bitstring to its “corresponding ideal probability computed via simulation on a classical computer” to ascertain that the quantum computer was working correctly.

“We made a lot of design choices in the development of our processor that are really advantageous,” said Chiaro. Among these advantages, he said, are the ability to experimentally tune the parameters of the individual qubits as well as their interactions.

While the experiment was chosen as a proof-of-concept for the computer, the research has resulted in a very real and valuable tool: a certified random number generator. Useful in a variety of fields, random numbers can ensure that encrypted keys can’t be guessed, or that a sample from a larger population is truly representative, leading to optimal solutions for complex problems and more robust machine learning applications. The speed with which the quantum circuit can produce its randomized bitstring is so great that there is no time to analyze and “cheat” the system.

“Quantum mechanical states do things that go beyond our day-to-day experience and so have the potential to provide capabilities and application that would otherwise be unattainable,” commented Joe Incandela, UC Santa Barbara’s vice chancellor for research. “The team has demonstrated the ability to reliably create and repeatedly sample complicated quantum states involving 53 entangled elements to carry out an exercise that would take millennia to do with a classical supercomputer. This is a major accomplishment. We are at the threshold of a new era of knowledge acquisition.”

Looking ahead

With an achievement like “quantum supremacy,” it’s tempting to think that the UC Santa Barbara/Google researchers will plant their flag and rest easy. But for Foxen, Chiaro, Martinis and the rest of the UCSB/Google AI Quantum group, this is just the beginning.

“It’s kind of a continuous improvement mindset,” Foxen said. “There are always projects in the works.” In the near term, further improvements to these “noisy” qubits may enable the simulation of interesting phenomena in quantum mechanics, such as thermalization, or the vast amount of possibility in the realms of materials and chemistry.

In the long term, however, the scientists are always looking to improve coherence times, or, at the other end, to detect and fix errors, which would take many additional qubits per qubit being checked. These efforts have been running parallel to the design and build of the quantum computer itself, and ensure the researchers have a lot of work before hitting their next milestone.

“It’s been an honor and a pleasure to be associated with this team,” Chiaro said. “It’s a great collection of strong technical contributors with great leadership and the whole team really synergizes well.”

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Longing2bhome Nov 02, 2019 11:57 AM
Achieving Quantum Supremacy

Every three years our knowledge doubles which is by 1950s standard ( knowledge doubled every 50 years) almost 17 times faster than now. Computations are a driving factor to this technology info revolution. Where to we get to go from here.? Are we there Yet? Are the perfect two sided coin questions I would like to ponder.

jqb Nov 01, 2019 11:06 AM
Achieving Quantum Supremacy

I'll get excited when it solves an actual pragmatic problem. Producing truly random bitstrings (which can be done in far easier and cheaper ways) ain't it.

yacht rocked Oct 31, 2019 05:17 PM
Achieving Quantum Supremacy

There was a good explainer on this in the NY Times yesterday. It's a big deal! Since no one's said it, Congrats to the entire team!

EastBeach Nov 02, 2019 02:51 PM
Achieving Quantum Supremacy

Good NYT article. It seems we're on the cusp of something greater than the delta between vacuum tubes and transistors. I expect one key towards applications will be to abstract away the complexities of the underlying technology so human engineers can focus on higher-level problem solving. Much like today where I don't have to worry about how to manipulate every little transistor in a circuit because I've got languages, compilers, synthesizers, and simulators to abstract away the details - but that will take time.

Channelfog Oct 31, 2019 10:33 AM
Achieving Quantum Supremacy

The real problem seems to be that this tech supersedes all cyber security measures, encryption, passwords, banking, the lot. The powers that be drool over the prospect of soon being able to read all new or archived encrypted mail. 1984 on steroids!

Factotum Oct 31, 2019 10:03 AM
Achieving Quantum Supremacy

Alex, we are where we are today because too many have abdicated personal responsiblity. No machine can fix that; in fact abdicating our best judgements to machines makes things worse.

Alexblue Nov 01, 2019 11:07 AM
Achieving Quantum Supremacy

Facty, where are we today? Higher global standard of living. Less war. Who is abdicating what responsibility? Who said we are giving decision making power to machines? Why do you people like you love to complain in the most nebulous generalities?

ChillinGrillin Oct 31, 2019 09:46 AM
Achieving Quantum Supremacy

Cool now Google can censor search results in authoritarian countries and collect and sell our information much quicker!

a-1590737303 Oct 31, 2019 09:32 AM
Achieving Quantum Supremacy

Is Google on UCSB campus? Where are Google staff offices located?

a-1590737303 Nov 01, 2019 10:17 AM
Achieving Quantum Supremacy

There are two locations. The original/first is behind the Hilton Garden Inn at Storke and Hollister at 6868 Cortona Drive, Unit B. It is this location where most of the manufacturing took place in the produced video. The second location is 5383 Hollister in the old Mentor building, just west of Goleta Cottage Hospital.

a-1590737303 Oct 31, 2019 09:21 AM
Achieving Quantum Supremacy

Unfathomable math. A computation which cannot be tested in real time. All for what? So Google can dive deeper into the psyche of man and unfold habits, patterns and expectations? What is the end game here? Oh I'm sure it'll be sold as some wonderful benefit for the masses. Yet all disguised in some herculean effort to formulate God like solutions in the eye of man.

Alexblue Oct 31, 2019 09:30 AM
Achieving Quantum Supremacy

253--would you prefer that humanity hit pause on knowledge and research right now? You good with where we are?

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