Establishing World-Record Coherence Times on Nuclear Spin qubits made from neutral atoms

Mickey McDonald, Senior Quantum Engineer

Coherence Times Matter

When building a quantum computer, the need to isolate qubits from environmental effects must be balanced against the need to engineer site-specific, controllable interactions with external fields. In our paper recently published in Nature Communications, we show results from our first-generation quantum computing system called Phoenix, which successfully navigates these competing requirements while demonstrating the capability to load more than 100 qubits. The most notable achievement we describe in this paper is the long coherence times of each of our qubits. Coherence is a term used to describe how long a qubit maintains its quantum state or encoded information. It’s important because longer coherence times mean fewer limitations on running deep circuits, and error-correction schemes have more time to detect and correct errors through mid-circuit measurements. On Phoenix, we set a new high water mark for coherence time.

Ramsey-echo measurements performed on an array of 21 qubits exhibit high contrast across tens of seconds, indicating a dephasing rate of T2echo = 40 +/- 7 seconds - the longest coherence time ever demonstrated on a commercial platform.

Achieving long coherence times requires that a qubit interact minimally with its environment, but this requirement often comes with a drawback: it is usually the case that the more weakly a qubit interacts with its environment, the more difficult it is to couple that qubit to whatever control fields are being used to drive interactions required to perform quantum computation. We manage these competing requirements by using a clever choice of neutral atom-based qubit, and by performing single-qubit control using software-configurable dynamic lasers which can be steered and actuated with sub-micron spatial accuracy and sub-microsecond timing precision.

Simultaneous Control of Qubits 

Our software-configurable optical control scheme allows Phoenix to simultaneously drive arbitrary single-qubit gate operations on all qubits within a single column or row in parallel, while at the same time maintaining coherence times longer than any yet demonstrated on a commercial platform, with a measured T2echo = 40 +/- 7 seconds.

A high-level drawing of Phoenix. Qubits are trapped within a vacuum cell and controlled using software-configurable dynamic lasers projected through a high-numerical aperture microscope objective. Readout is performed by collecting scattered light through the same microscope objective onto a camera.

Our system encodes quantum information, i.e. the qubit states |0> and |1>, in two of the nuclear spin states of a single, uncharged strontium atom. This kind of qubit encoding has two key advantages. First, because both qubit states exist in the electronic ground state, the time it takes for one state to spontaneously decay to the other (AKA the spin-relaxation time “T1”) is effectively infinite. We demonstrate this on Phoenix by making spin relaxation measurements out to several seconds and confirming that the relative populations in each state remain unchanged to the limits of measurement precision.

The spin relaxation time (known as “T1”) describes how long it takes for a qubit initially prepared in one qubit state to decay to another. A short T1 would manifest as a line which starts near 1 and drifts downward. That our measured population can be fit with a horizontal line with no apparent downward drift indicates that our spin relaxation time is far longer than our longest measurement time.

The second key advantage of nuclear spin qubits is that because the qubit states have such similar energies, they are nearly identically affected by external fields. This means that perturbations, such as those induced by externally applied trapping light, will affect both qubit states in the same way. Because these perturbations are common-mode, they do not impact the system’s overall coherence - a feature which fundamentally enables our world-record coherence times.

Our Path Forward

This paper describing Phoenix demonstrates several key technological innovations necessary for the construction of a large-scale, commercial quantum computer: long coherence times, the ability to drive arbitrary single qubit operations across large portions of the array in parallel, and the ability to trap 100+ qubits (and far beyond in the future). As we develop our second-generation quantum computers, we will build on the proven architecture and successes demonstrated on Phoenix to scale up to systems with fidelities and qubit numbers high enough to solve problems that cannot be solved with classical computers. Stay tuned and sign up for our Tech Perspectives blog series to learn more!

The Quantum Effect - Capgemini Invent #FutureSight Podcast

The Quantum Effect: What impact will #quantum computing have on business, the talent market, and more as its use cases evolve? Listen in to an insightful conversation with Rob HaysJulian van Velzen and Olivia Lanes, PhD in this Capgemini Invent podcast. 

Quantum Computing Value as it Scales to Thousands of Qubits

Rob Hays, CEO
Rob Hays discusses Atom Computing’s architecture of nuclear-spin qubits made from neutral atoms. He shares how the technology will enable large-scale quantum computers and the necessity for coherent, error-corrected systems -- exploring applications and use-cases that quantum computing can help solve as the system scales to 1,000s of qubits and beyond.

Building Scalable Quantum Computers from Arrays of Neutral Atoms

Krish Kotru, Quantum Engineering Manager

Arrays of neutral atoms have emerged as a more promising platform for scalable quantum computation due to the rapid advancements in optical trapping and controlling of individually trapped atoms. Krish discusses the technology enabling the assembly of such arrays and recent results demonstrating parallel coherent control and world-record coherence times. He also surveys ongoing work demonstrating interactions between atoms in Rydberg states that enable high-quality two qubit gates.

Highly Coherent Qubits and the Path to Error Correction

Jonathan King, Co-Founder & Chief Scientist

Realizing the full value of quantum computing will require error correction to suppress the errors intrinsic to quantum systems. Practically, this requires high-quality qubits in a sufficiently large quantity. Jonathan discusses the application of error correction in quantum computing and describes a path to error correction with neutral atoms.

How Boutique Quantum Specialist Firms are Addressing Industry Applications with Atom Computing

Denise Ruffner, Chief Business Officer, Atom Computing
Markus Braun, Founder and Managing Director, JoS Quantum
Rafael Sotelo, Co-Founder, Quantum South
Tennin Yan, QunaSys

Quantum has the potential to solve challenging computation challenges across a variety of industries. While there is growing consensus on the types of problems addressable through quantum (optimization, machine learning acceleration, and simulation), the development of solutions for individual industries and organizations will require focused attention and development by domain experts. In this panel, we will discuss how boutique quantum specialist firms are addressing real world problems and how they will leverage the latest quantum hardware advances to bring value to organizations.

Kayleigh Gives a Deep-Dive on our Quantum Computer on the QuBites Podcast

Robin Coxe Talks About the Company, and the Intersection of Quantum and Classical Computing on QuBites Podcast

Employee Spotlight: Miro Urbanek, Senior Quantum Applications Engineer

We sat down with Miro Urbanek to talk about his quantum journey and why he's passionate about the work we are doing here at Atom Computing.

Why did you decide to get into quantum computing - what is your passion with this field?

Miro: I used to work on physical simulations that ran on classical computers before working in quantum computing. Some of my simulations were too slow even on supercomputers. I realized that classical computers could never solve these problems efficiently. However, quantum computers can and that's why I decided to turn my attention to them.

What is the most interesting thing you’ve learned since working in this field?

Miro: I tried to find an argument why quantum computing is fundamentally impossible, but I couldn't find any such reason.

What gets you excited about how quantum computing could change the world? What is a problem you are passionate about that quantum computing may help solve-for in the future?

Miro: I'm interested in simulations of physics, chemistry, and other natural phenomena. These are really hard applications for classical computers, especially if they involve quantum effects. In particular, I want to help researchers who design and explore novel materials to use quantum computers. Improved materials can lead to better batteries and other advances in energy production and storage. Applications of quantum computers are still largely unexplored. We'll only discover their full potential in the future.

Tell us why you chose to work at Atom Computing?

Miro: Neutral atoms are the most promising platform for scalable quantum computers. In fact, there have been many experiments with neutral atoms that are impossible to simulate on classical computers today. I also liked the expertise and spirit of the people working at Atom Computing.

What is one piece of advice you’d offer someone in high school or college considering getting into this field?

Miro: Learn math. Numbers rule the universe!

Employee Spotlight: Katy Barnes, Principal Hardware Engineer

We sat down with Katy Barnes to talk about her career path to quantum and why she enjoys working in this field and at Atom Computing on the Control Systems Engineering team.

Why did you decide to get into quantum computing - what is your obsession with this field?

Katy: Honestly, I didn't really set out to work in quantum computing. The biggest draw for me to Engineering, in general, was that the field is always changing and I'd be forever learning. My dream was that I would have the opportunity to be part of a team that was working on world-changing, cutting-edge technology, and quantum computing is the epitome of both. I count myself fortunate to be a part of Atom Computing and I'm very excited to see what we can create together!

What is the most interesting thing you’ve learned since working in this field?

Katy: The Physics behind quantum computing is fascinating; so is pondering the ways it will transform any industry it touches. Before joining Atom Computing, I envisioned Quantum Physics as this weird science that challenged the Physics principles we are comfortable with. Many of us have heard of Schrödinger's cat, but truly wrapping your mind around the idea of uncertainty and how it can be used as a computing tool is incredibly difficult. It’s not something I studied in depth in school (and I still think it’s weird), but the more I learn about how it works, the more enthralled I am.

Thinking about how classical computing changed over the years makes me very excited to see how the quantum computing industry will grow and change.  

What gets you excited about how quantum computing could change the world? What is a problem you are passionate about that quantum computing may help solve-for in the future?

Katy: I believe that quantum computing has the potential to transform almost everything in this world. I am most excited about how it could change the healthcare industry. I cannot even fathom what new treatments or cures could be created to battle the sickness and disease that plague today’s society. I’m sure there are many ways we haven’t even thought of that quantum computing could help to diagnose and treat various medical issues. 

Tell us why you chose to work at Atom Computing?

Katy: One of the major things that drove me to work for Atom Computing, in particular, is that “humble” was one of the requirements in the job description. That one word says to me that not only will I be working with brilliant people on very cool, very cutting edge technology, but I will be working with a team that doesn’t let egos get in the way of progress—that we all will have the same goal.  And now that I have worked with the team, I know that it’s true!

What is one piece of advice you’d offer someone in high school or college considering getting into this field?

Katy: Don’t be afraid to ask questions. If you don’t understand something, keep asking questions until you do understand. In the STEM field, each new topic tends to build on something else you’ve learned, so it’s easy to get lost. Make sure you don’t just memorize, but understand the why and how—it makes it easier to apply the concepts to real-world problems. It can be intimidating to be in a room full of smart people who all seem to get it, but I can guarantee that there are several people in the room that would be happy that you asked that question. Never stop learning!