First successful demonstration of quantum error correction of qudits for quantum computers

Good news!

"... A recent study by researchers from Yale University published in Nature created qudits—a quantum system that holds quantum information and can exist in more than two states. Using a qutrit (3-level quantum system) and a ququart (4-level quantum system), the researchers demonstrated the first-ever experimental quantum error correction for higher-dimensional quantum units using the Gottesman–Kitaev–Preskill (GKP) bosonic code. ...

The experiment pushed past the break-even point for error correction, showcasing a more practical and hardware-efficient method for QEC by harnessing the power of a larger Hilbert space. ..."

From the abstract:

"Hilbert space dimension is a key resource for quantum information processing. Not only is a large overall Hilbert space an essential requirement for quantum error correction, but a large local Hilbert space can also be advantageous for realizing gates and algorithms more efficiently. As a result, there has been considerable experimental effort in recent years to develop quantum computing platforms using qudits (d-dimensional quantum systems with d > 2) as the fundamental unit of quantum information.

Just as with qubits, quantum error correction of these qudits will be necessary in the long run, but so far, error correction of logical qudits has not been demonstrated experimentally.

Here we report the experimental realization of an error-corrected logical qutrit (d = 3) and ququart (d = 4), which was achieved with the Gottesman–Kitaev–Preskill bosonic code. Using a reinforcement learning agent, we optimized the Gottesman–Kitaev–Preskill qutrit (ququart) as a ternary (quaternary) quantum memory and achieved beyond break-even error correction with a gain of 1.82 ± 0.03 (1.87 ± 0.03). This work represents a novel way of leveraging the large Hilbert space of a harmonic oscillator to realize hardware-efficient quantum error correction."

First successful demonstration of quantum error correction of qudits for quantum computers

Quantum error correction of qudits beyond break-even (open access)

Fig. 1: Stabilizing GKP qudits.

Amazon's new Ocelot chip brings us closer to building a practical quantum computer

Good news! On the heels of Microsoft's announcement (see my blog post). 

2025 really shapes up to be a of quantum computing takeoff as was frequently suggested.

"Today, Amazon Web Services (AWS) announced Ocelot, a new quantum computing chip that can reduce the costs of implementing quantum error correction by up to 90%, compared to current approaches. Developed by the team at the AWS Center for Quantum Computing at the California Institute of Technology, Ocelot represents a breakthrough in the pursuit to build fault-tolerant quantum computers capable of solving problems of commercial and scientific importance that are beyond the reach of today’s conventional computers. ...

Ocelot was designed from the ground up with error correction “built in.” ...

Ocelot: Fast facts

• Ocelot is a prototype quantum computing chip, designed to test the effectiveness of AWS’s quantum error correction architecture.
• It consists of two integrated silicon microchips. Each chip has an area of roughly 1cm2. They are bonded one on top of the other in an electrically-connected chip stack.
• On the surface of each silicon microchip are thin layers of superconducting materials that form the quantum circuit elements.
• The Ocelot chip is composed of 14 core components: five data qubits (the cat qubits), five ‘buffer circuits’ for stabilizing the data qubits, and four additional qubits for detecting errors on the data qubits.
• The cat qubits store the quantum states used for computation. To do so, they rely on components called oscillators, which generate a repetitive electrical signal with steady timing.
• Ocelot’s high-quality oscillators are made from a thin film of superconducting material called Tantalum. AWS material scientists have developed a specific way of processing Tantalum on the silicon chip to boost oscillator performance.

..."

"... Ocelot achieves the following major technical advances: 

• The first realization of a scalable architecture for bosonic error correction, surpassing traditional qubit approaches to reducing error correction overhead;
• The first implementation of a noise-biased gate — a key to unlocking the type of hardware-efficient error correction necessary for building scalable, commercially viable quantum computers;
• State-of-the-art performance for superconducting qubits, with bit-flip times approaching one second in tandem with phase-flip times of 20 microseconds.

..."

"... a new quantum chip architecture for suppressing errors using a type of qubit known as a cat qubit. Cat qubits were first proposed in 2001, and, since then, researchers have developed and refined them. Now, the AWS team has put together the first scalable cat qubit chip that can be used to efficiently reduce quantum errors. ...

Due to the complexity of superposition found in qubits, they can have two types of errors:

bit flips, as in the classical digital systems, and

phase flips, in which the qubit states of 1 and 0 become out of phase (or out of sync) with each other.

Researchers have developed many strategies to handle both error types in quantum systems, but the methods require qubits to have a significant number of backup partners. In fact, current qubit technologies may require thousands of additional qubits to provide the desired level of protection from errors. ...

The team's new scheme relies on a type of qubit formed from superconducting circuits made of microwave oscillators, in which the 1 and 0 states representing the qubit are defined as two different large-scale amplitudes of oscillation. This makes the qubit states very stable and impervious to bit-flip errors. ...

In fact, the name "cat" qubits refers to the ability of these qubits to take on two very large, or macroscopic states, at the same time—just like the famous cat in Erwin Schrödinger's [cat] thought experiment, which can be both dead and alive simultaneously. ...

The Ocelot chip achieves this by combining five cat qubits, along with special buffer circuits to stabilize their oscillation, and four ancillary qubits to detect phase errors. ..."

From the abstract:

"To solve problems of practical importance, quantum computers probably need to incorporate quantum error correction, in which a logical qubit is redundantly encoded in many noisy physical qubits.

The large physical-qubit overhead associated with error correction motivates the search for more hardware-efficient approaches. Here, using a superconducting quantum circuit, we realize a logical qubit memory formed from the concatenation of encoded bosonic cat qubits with an outer repetition code of distance d = 5.

A stabilizing circuit passively protects cat qubits against bit flips. The repetition code, using ancilla transmons for syndrome measurement, corrects cat qubit phase flips.

We study the performance and scaling of the logical qubit memory, finding that the phase-flip correcting repetition code operates below the threshold. The logical bit-flip error is suppressed with increasing cat qubit mean photon number, enabled by our realization of a cat-transmon noise-biased CX gate.

The minimum measured logical error per cycle is on average 1.75(2)% for the distance-3 code sections, and 1.65(3)% for the distance-5 code. Despite the increased number of fault locations of the distance-5 code, the high degree of noise bias preserved during error correction enables comparable performance.

These results, where the intrinsic error suppression of the bosonic encodings enables us to use a hardware-efficient outer error-correcting code, indicate that concatenated bosonic codes can be a compelling model for reaching fault-tolerant quantum computation."

Amazon's new Ocelot chip brings us closer to building a practical quantum computer "New 'Ocelot' chip uses scalable architecture for reducing error correction by up to 90% and accelerating the development of real-world quantum computing applications."

Amazon announces Ocelot quantum chip (technical report) "Prototype is the first realization of a scalable, hardware-efficient quantum computing architecture based on bosonic quantum error correction."

New Ocelot Chip Makes Strides in Quantum Computing (CalTech's corresponding news release) "Scientists based at the AWS Center for Quantum Computing on Caltech's campus have made a leap forward in figuring out how to suppress errors in quantum computers, a pesky problem that continues to be the greatest hurdle to building the machines of the future."

Hardware-efficient quantum error correction via concatenated bosonic qubits (open access)

The pair of silicon microchips that compose the Ocelot logical-qubit memory chip.

Fig. 1: Repetition code of bosonic qubits.

A dilution refrigerator at the AWS Center for Quantum Computing. Quantum computers require these cooling devices to maintain the quantum chips at ultra-cold temperatures.

Quantinuum Successfully Teleports a Logical Qubit

Good news! More advances in quantum computing!

"... The most exciting thing about the new results ... is that they demonstrate it’s possible to actually compute on an error-corrected quantum computer. Previous experiments have shown that it’s possible to use error correction to “keep quantum information alive ...

This simplicity allowed them to teleport logical qubits with a fidelity of 97.5 percent, significantly exceeding the target set by IARPA. Not all quantum computers can use transversal gates, however, as many architectures feature qubits that are fixed in place, including those that rely on superconducting qubits. So the team also tested another approach known as “lattice surgery,” which makes it possible to entangle logical qubits without direct interaction between all of their physical qubits. However, the approach is more complicated and involves considerably more operations, says Hayes, so they were able to only achieve fidelities of 85.1 percent. ..."

"... Quantinuum’s demonstration marks the first time that an arbitrary quantum state has been teleported at the logical level (using a quantum error correcting code). This means that instead of teleporting the quantum state of a single physical qubit we have teleported the quantum information encoded in an entangled set of physical qubits, known as a logical qubit. In other words, the collective state of a bunch of qubits is teleported from one set of physical qubits to another set of physical qubits. ..."

From the editor's summary and abstract:

"Editor’s summary

Quantum entanglement and the teleportation of a quantum state across the processor are key ingredients in quantum computing. The fragility of the quantum states, however, requires error correction codes to ensure their faithful processing. Using a trapped-ion platform consisting of up to 30 trapped ions, the Quantinuum H2 quantum processor, ... demonstrate the fault-tolerant teleportation of quantum states. The implemented error-correcting color code effectively stabilizes the qubits, allowing quantum teleportation to be carried out in a fault-tolerant manner. The results are promising for trapped-ion–based quantum computing platforms. ...

Abstract

Quantum state teleportation is commonly used in designs for large-scale quantum computers. Using Quantinuum’s H2 trapped-ion quantum processor, we demonstrate fault-tolerant state teleportation circuits for a quantum error correction code—specifically the Steane code. The circuits use up to 30 qubits at the physical level and employ real-time quantum error correction. We conducted experiments on several variations of logical teleportation circuits using both transversal gates and lattice surgery. We measured the logical process fidelity to be 0.975 ± 0.002 for the transversal teleportation implementation and 0.851 ± 0.009 for the lattice surgery teleportation implementation as well as 0.989 ± 0.002 for an implementation of Knill-style quantum error correction."

Quantinuum Successfully Teleports a Logical Qubit - IEEE Spectrum "The feat could enable large-scale, fault-tolerant quantum computers"

Quantinuum achieves moonshot years ahead of schedule, demonstrating fault-tolerant high-fidelity teleportation of a logical qubit (original news release)

High-fidelity teleportation of a logical qubit using transversal gates and lattice surgery (no public access)

The H2 processor is housed in an ultrahigh-vacuum chamber

Microsoft and Quantinuum say they’ve ushered in the next era of quantum computing

Good news!

"... Today [4/3/2024], Microsoft is announcing a critical breakthrough that advances the field of quantum computing by improving the logical error rate by 800x when compared to the error rate on corresponding physical qubits, thus creating the most reliable logical qubits to date. ...

The results presented here were achieved by coupling Microsoft’s qubit-virtualization system with Quantinuum’s specialized hardware. Quantinuum’s H-Series ion-trap qubits and unique Quantum Charged Coupled Device architecture have an excellent two-qubit gate fidelity of 99.8%. By applying our qubit-virtualization system to their qubits, we have been able to run 14,000 independent instances so far without a single error. Our sophisticated system has error diagnostics and corrections built in, allowing us to easily determine which errors need to be fixed and how to fix them.

With our qubit-virtualization system, we were able to create four highly reliable logical qubits from only 30 physical qubits of the available 32 on Quantinuum’s machine. When entangled, these logical qubits exhibited a circuit error rate of 10-5 or 0.00001, which means they would experience an error only once in every 100,000 runs. That is an 800x improvement over the circuit error rate of 8×10-3 or 0.008, measured from entangled physical qubits. This result was achieved through a combination of advanced runtime error diagnostics with computational run rejection and error correction. ..."

From the abstract:

"The promise of quantum computers hinges on the ability to scale to large system sizes, e.g., to run quantum computations consisting of roughly more than 100 million operations fault-tolerantly. This in turn requires suppressing errors to levels inversely proportional to the size of the computation. As a step towards this ambitious goal, we present experiments on a trapped-ion QCCD processor where, through the use of fault-tolerant encoding and error correction, we are able to suppress logical error rates to levels below the physical error rates. In particular, we show Bell states encoded in the [[7,1,3]] code with error rates 9.8 to 500 times lower than at the physical level, and Bell states encoded in a [[12,2,4]] code with error rates 4.7 to 800 times lower than at the physical level, depending on the judicious use of post-selection. Moreover, we demonstrate repeated error correction with the [[12,2,4]] code, with logical error rates below physical circuit baselines corresponding to repeated CNOTs, and show evidence that the error rate per error correction cycle, which consists of over 100 physical CNOTs, approaches the error rate of two physical CNOTs. These results signify an important transition from noisy intermediate scale quantum computing to reliable quantum computing, and demonstrate advanced capabilities required for large-scale fault-tolerant quantum computing."

Microsoft and Quantinuum say they’ve ushered in the next era of quantum computing | TechCrunch

How Microsoft and Quantinuum achieved reliable quantum computing (original news release) By applying an innovative qubit-virtualization system to ion-trap hardware, Microsoft and Quantinuum were able to create four highly reliable logical qubits from only 30 physical qubits, while demonstrating an 800x improvement in error rate.

Demonstration of logical qubits and repeated error correction with better-than-physical error rates (open access)

Figure 1: A depiction of the preparation we used to entangle qubits. The portion inside the dashed line is a rough representation of the circuit used to create the entangled state. A and B represent measurements that can be applied to each half of the state. In the absence of errors, the outcome on one half should agree with the outcome on the other half, if the types of measurement applied to each half are the same. Impressively, after this procedure was run 14,000 times, there were no disagreements between the measurement outcomes.

Air Canada has to honor a refund policy its chatbot made up

Growing up in the age of AI! 

Lesson learnt: Don't let AI get near your money! 😊

Remember: AI is being developed by a large number of leftist researchers!

"The airline was forced to offer a customer a partial refund after its customer service chatbot inaccurately explained the company’s bereavement travel policy. Expect more cases like this as long as the tech sector sells chatbots that still make things up and have security flaws. (Wired)"

Bans on deepfakes take us only so far—here’s what we really need

Researchers create first logical quantum processor with quantum error correction and fault tolerance

Good news! Amazing stuff! Could be a major breakthrough!

"... The team ... has created the first programmable, logical quantum processor, capable of encoding up to 48 logical qubits, and executing hundreds of logical gate operations, a vast improvement over prior efforts. ...

The system is the first demonstration of large-scale algorithm execution on an error-corrected quantum computer, heralding the advent of early fault-tolerant, or reliably uninterrupted, quantum computation. ...
the ideas of quantum error correction and fault tolerance, long theorized, are starting to bear fruit. ...

The ... team’s breakthrough builds on several years of work on a quantum computing architecture known as a neutral atom array ... It is now being commercialized by QuEra ..."

From the abstract:

"Suppressing errors is the central challenge for useful quantum computing, requiring quantum error correction for large-scale processing. However, the overhead in the realization of error-corrected “logical” qubits, where information is encoded across many physical qubits for redundancy, poses significant challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Utilizing logical-level control and a zoned architecture in reconfigurable neutral atom arrays, our system combines high two-qubit gate fidelities, arbitrary connectivity, as well as fully programmable single-qubit rotations and mid-circuit readout Operating this logical processor with various types of encodings, we demonstrate improvement of a two-qubit logic gate by scaling surface code distance from d = 3 to d = 7, preparation of color code qubits with break-even fidelities, fault-tolerant creation of logical GHZ states and feedforward entanglement teleportation, as well as operation of 40 color code qubits. Finally, using three-dimensional [[8,3,2]] code blocks, we realize computationally complex sampling circuits with up to 48 logical qubits entangled with hypercube connectivity with 228 logical two-qubit gates and 48 logical CCZ gates. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling. These results herald the advent of early error-corrected quantum computation and chart a path toward large-scale logical processors."

Harvard researchers create first logical quantum processor — Harvard Gazette Key step toward reliable, game-changing quantum computing

Logical quantum processor based on reconfigurable atom arrays (no public access)

Doubling a qubit’s life, researchers prove a key theory of quantum physics

Amazing stuff! Could be a breakthrough! Extending classical error correction to quantum physics! Again machine learning was applied in this research!

"Researchers at Yale have for the first time, using a process known as quantum error correction, substantially extended the lifetime of a quantum bit — a long-sought-after goal and one of the trickiest challenges in the field of quantum physics. ...
decades after its theoretical foundations were proposed — that quantum error correction works in practice.  ...

Quantum systems, though, are fragile. They are bedeviled by a fundamental phenomenon of decoherence, a process in which the information stored in qubits quickly loses its quantum properties as a result of their interactions with the surrounding environment. 

Quantum error correction, which was theoretically discovered in 1995, offers a means to combat this decoherence. Employing redundancy, it protects the quantum bit of information by encoding it in a system larger than what, in principle, is needed to represent a single qubit. ..."

From the abstract:

"The ambition of harnessing the quantum for computation is at odds with the fundamental phenomenon of decoherence. The purpose of quantum error correction (QEC) is to counteract the natural tendency of a complex system to decohere. This cooperative process, which requires participation of multiple quantum and classical components, creates a special type of dissipation that removes the entropy caused by the errors faster than the rate at which these errors corrupt the stored quantum information. Previous experimental attempts to engineer such a process faced the generation of an excessive number of errors that overwhelmed the error-correcting capability of the process itself. Whether it is practically possible to utilize QEC for extending quantum coherence thus remains an open question. Here we answer it by demonstrating a fully stabilized and error-corrected logical qubit whose quantum coherence is substantially longer than that of all the imperfect quantum components involved in the QEC process, beating the best of them with a coherence gain of G = 2.27 ± 0.07. We achieve this performance by combining innovations in several domains including the fabrication of superconducting quantum circuits and model-free reinforcement learning."

Doubling a qubit’s life, researchers prove a key theory of quantum physics | Yale School of Engineering & Applied Science

Real-time quantum error correction beyond break-even (no public access)

Fig. 1: Experimental system

Israel Joins the Quantum Computing Club

Impressive!

"... Prof. Roee Ozeri of the Weizmann Institute of Science begs to differ: “One of the world’s first computers, WEIZAC, was built here in the 1950s, when all Israel had was swamps and camels. Today Israel is a technological empire; there’s no reason we shouldn’t be front-runners in the quantum computing race.” ...
in building a quantum computer – one of about 30 such machines in the world, and one of less than 10 to rely on an advanced technology known as ion traps. An even larger computer is already in the works ...

Despite this expansion of research, substantial challenges remain. One of the greatest obstacles is the extreme sensitivity of quantum computers to environmental noise, which stands in the way of building large, complex systems. In a project ... addressed this challenge by introducing two innovations, both successfully implemented in the quantum computer the researchers have built in their lab. ...
To prevent this from happening, the Weizmann researchers developed a pattern of laser pulses that keeps the logic gates robust and stable [in the presence of noise]. ...
a camera-based array that detects all the qubits simultaneously. Then, to protect the system’s quantum nature, they concealed some of the qubits from the camera. They also developed a way to overcome the slow-down in data processing that had been associated with camera-based arrays: They added electronic circuits that rapidly read out and process the cameras’ information, speeding up error correction. ..."

From the abstract:

"... Chains of ions held in a linear Paul trap are a promising platform for constructing such quantum computers, due to their long coherence times and high quality of control. Here, we report on the construction of a small five-qubit universal quantum computer using 88Sr+  ions in a radio-frequency (rf) trap. All basic operations, including initialization, quantum logic operations, and readout, are performed with high fidelity. Selective two-qubit and single-qubit gates, implemented using a narrow-line-width laser, comprise a universal gate set, allowing realization of any unitary on the quantum register. We review the main experimental tools and describe in detail unique aspects of the computer: the use of robust entangling gates and the development of a quantum coherent feedback system through electron-multiplying CCD camera acquisition. The latter is necessary for carrying out quantum error-correction protocols in future experiments."

Israel Joins the Quantum Computing Club - Space & Physics | Weizmann Wonder Wander - News, Features and Discoveries Weizmann Institute of Science researchers present Israel’s first quantum computer

Trapped-Ion Quantum Computer with Robust Entangling Gates and Quantum Coherent Feedback (open access)

A Molecular Approach to Quantum Computing

Recommendable!

"In the new paper, this concept [error-correcting scheme, known as GKP] is applied to rotating molecules in superposition. If the orientation or angular momentum of the molecule shifts by a small amount, those shifts can be simultaneously corrected. ... "The appeal of molecules is that they are very complex structures that can be very densely packed," says Covey. "If we can figure out how to utilize molecules in quantum computing, we can robustly encode information and improve the efficiency in which qubits are packed." ..."

"... polyatomic molecule ..."
Sometimes scientists try to dazzle their audience with fancy language. Are not basically all molecules polyatomic by definition?

A Molecular Approach to Quantum Computing | www.caltech.edu New research demonstrates how the use of molecules in quantum computing leads to fewer errors

Here is the link to the underlying research paper (open access):
Robust encoding of a qubit in a molecule