The quantum computer race has been hot for a few years now, with drug discovery, materials science, optimization, machine learning, and cryptography being just a few of the areas that will be revolutionized by its advancements. But despite all the progress, building quantum computers that solve real-world problems has been held back by three big challenges:
Now, a team at Chalmers University of Technology in Sweden has taken a significant step in addressing these challenges and accelerating the development of practical quantum computers. They recently published a new method in the journal Nature for manipulating quantum information using tunable nonlinearity in superconducting circuits. This allows for complex operations on multi-dimensional quantum states to be performed faster and more accurately than ever before.
At the heart of quantum computing is the quantum bit, or qubit, the fundamental unit of quantum information. Unlike classical bits, which are either 0 or 1, qubits can be both 0 and 1 and everything in between. Qubits can also be entangled with each other, allowing quantum computers to perform some calculations much faster than classical computers.
However, reaching this capability has been a significant challenge. One of the biggest issues is the fragility of quantum states. Qubits are sensitive to their environment and quickly lose their quantum properties through decoherence, introducing errors into the quantum computation and limiting the depth of computations.
Another major problem is scaling. As more qubits are added to a quantum processor, it becomes harder to control the interactions between them and to implement the quantum gates. This is because the control systems and cross-talk between qubits become more complex.
And theres a trade-off between coherence and controllability. Techniques that make qubits more coherent, like error correction codes, require more resources and limit some operations. Systems that have more control over individual qubits, like trapped ions or superconducting circuits, are noisier and more prone to decoherence.
Think of a qubit as a blue lamp that, quantum mechanically, can be both switched on and off simultaneously. In contrast, a continuous variable quantum system is like an infinite rainbow, offering a seamless gradient of colors. This illustrates its ability to access a vast number of states, providing far richer possibilities than the qubit's two states.
Axel Eriksson, researcher in quantum technology at Chalmers University of Technology and lead author of the study
Click here to learn about the current state of quantum computing.
The Chalmers University team, led by Drs. Axel M. Eriksson and Simone Gasparinetti have solved these problems by using superconducting circuits. Theyve developed a special component called a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) resonator.
SNAILs are superconducting circuit elements with strong, tunable nonlinearity. Its a superconducting loop with Josephson junctions, thin insulating barriers that allow Cooper pairs (bound pairs of electrons) to tunnel through. By arranging the junctions asymmetrically, theyve made a circuit element with nonlinear inductance.
We have made a system that does complex operations on a multi-state quantum system faster than ever before.
Senior author Dr. Simone Gasparinetti, leader of the 202Q-lab at Chalmers University
The key thing the Chalmers team did was to put a SNAIL resonator inside a superconducting microwave cavity, which is a bosonic mode for encoding quantum information. They applied microwave pulses to this hybrid system and activated and deactivated the nonlinearity in the SNAIL to perform all sorts of quantum operations fast and accurately.
One of the unique things about the Chalmers teams approach is that it goes beyond the qubit paradigm and uses continuous-variable (CV) quantum states. In a CV quantum system, information is encoded in the amplitude and phase quadratures of a harmonic oscillator, like a microwave cavity field. Those quadratures can take on a continuous range of values, not just 0 and 1 like qubits. According to senior author Dr. Simone Gasparinetti, leader of the 202Q-lab at Chalmers University:
We have created a system that enables extremely complex operations on a multi-state quantum system, at an unprecedented speed.
The CV approach has advantages over discrete-variable quantum computing. (i) One, a single CV mode can encode multiple qubits worth of information, which means less hardware for fault-tolerant quantum computing. (ii) Two, the consciousness of CV states allows for better error correction codes, which are needed for quantum computing with noise and decoherence.
However, a big problem in CV quantum computing is non-Gaussian operations, which are needed for universal quantum computing. Gaussian operations like displacement and squeezing of the oscillator state can be done with linear optical elements or microwave circuits, but thats not enough for quantum speedup because it can be classically simulated.
Non-Gaussian operations require nonlinear interactions, which are much harder to make and control. Previous attempts to combine CV modes with nonlinear elements have been foiled by the Kerr effect, which messes up the quantum information and reduces the operation fidelity.
The Chalmers team has solved this by engineering the nonlinearity inside the SNAIL resonator. They operate the SNAIL at a so-called Kerr-free point, where the unwanted Kerr nonlinearity is suppressed, and the third-order nonlinearity thats needed for non-Gaussian operations is preserved.
Our community has often tried to keep superconducting elements away from quantum oscillators, not to scramble the fragile quantum states. In this work, we have challenged this paradigm. By embedding a controlling device at the heart of the oscillator we were able to avoid scrambling the many quantum states while at the same time being able to control and manipulate them. As a result, we demonstrated a novel set of gate operations performed at very high speed.
Simone Gasparinetti
To show what they can do, theyve made a universal gate set on their SNAIL-resonator platform. That includes Gaussian gates like displacement and squeezing and a cubic phase gate, which is non-Gaussian.
The Gaussian gates were made by applying microwave pulses at specific frequencies to the SNAIL circuit. Driving at the fundamental frequency gives displacement, and driving at twice the fundamental frequency gives squeezing. Thats for preparing and manipulating coherent and squeezed states, which are the blocks for CV quantum information processing.
The cubic phase gate was made by combining a trisqueezing interaction (driving at three times the fundamental frequency) with drives at lower frequencies. That applies a nonlinear phase shift to the oscillator state thats proportional to the cube of the amplitude, hence the name cubic phase.
The cubic phase gate is needed for universal CV quantum computing because it makes highly non-classical states like Gottesman-Kitaev-Preskill (GKP) states, which are for fault-tolerant quantum error correction. The cubic phase gate with Gaussian gates makes a deterministic non-Gaussian state called the cubic phase state.
The gates made by the Chalmers team were made with pulses as short as tens of nanoseconds. Thats 10-100 times faster than previous implementations with dispersive qubit-oscillator couplings. Thats because of the strong nonlinearity in the SNAIL resonator.
Another example is the Chalmers team using their universal gate set to make a highly non-classical quantum state called a cubic phase state. Cubic phase states are needed for quantum error correction, quantum metrology, and CV measurement-based quantum computing.
Cubic phase state preparation was made by applying gates to the ground state (vacuum) of the SNAIL resonator. First, a 20-ns squeezing gate was applied to make a squeezed vacuum state. Then, a 40-ns cubic phase gate was applied to that squeezed state, and voil, a cubic phase state with a cubicity of 0.11.
The state was characterized with Wigner tomography, which makes a phase-space distribution of the quantum state. The Wigner function was strongly negative, which is non-classical and cannot be seen in any classical oscillator state.
The fidelity of the cubic phase state with respect to the target state was 92%. They showed that the cubicity of the state can be increased by just extending the cubic phase gate duration. Thats much better than previous state preparation methods, which required a full re-optimization of the control sequence for each cubicity value.
While what the Chalmers team has done is already commendable, theres still more to be done:
One limitation of the quantum operations is the coherence time of the SNAIL resonator. They have coherence times of a few microseconds, which is enough for now, but longer coherence times will allow for more complex and deeper quantum circuits. Optimizing the SNAIL circuit parameters to reduce flux noise and shielding and filtering the microwave environment are ways to improve coherence.
This includes:
Click here to learn how quantum emitters and infrared lasers can help us build the next generation of quantum computers.
Another area to improve is scalability. The experiment was done with one SNAIL, but a large-scale quantum computer needs multiple SNAILs. To scale up, one could use multiple SNAILs, each connected to its own microwave cavity. This setup allows for the creation of multi-qubit gates and entangled states by designing the coupling between the cavities. However, that requires control over the fabrication and tuning of the SNAILs to be homogeneous and reproducible.
Besides scaling up the number of CV modes, we also need to scale up the number of photons in each mode. The SNAIL resonator's nonlinearity deviates from its ideal behavior at higher photon numbers, which limits the size of the computational Hilbert space.
One way to fix that is to use a multi-SNAIL design in which the nonlinearity of each SNAIL is engineered to cancel out at higher orders while preserving the lower-order interactions.
Other plausible advancements include:
Looking ahead, the Chalmers team wants to integrate their SNAIL-resonator platform with other quantum computing architectures to make hybrid systems. For example, SNAIL-mediated interactions can be used to entangle superconducting qubits and CV modes to make complex multi-qubit states. The fast and efficient CV gates in this work can be used for quantum error correction on encoded qubits, and that will make more robust and scalable quantum processors.
One exciting prospect to look forward to is integrating the SNAIL-resonator platform with optical quantum systems. Superconducting circuits are good for quantum computing, which operate at microwave frequencies and cryogenic temperatures, are good for quantum computing. In contrast, optical quantum systems, which function at room temperature, are ideal for long-distance quantum communication. By developing a quantum frequency converter, we can combine the best of both worlds to create a scalable and networked quantum computer.
What the Chalmers team has achieved is a major advancement for practical quantum computers. Theyve used tunable nonlinearity in superconducting circuits to develop a hardware-efficient and controllable quantum computer capable of rapidly and accurately performing complex operations on multidimensional quantum states.
This represents a new paradigm in CV-NISQ computing. SNAIL resonators can solve hard problems in quantum chemistry, optimization, and machine learning. As this technology matures and scales, it will open up applications that are not possible with classical computers.
However, building large-scale, fault-tolerant quantum computers still presents substantial challenges, including the coherence time of superconducting circuits, the number of qubits and CV modes, and interfaces between quantum computing platforms.
Despite these challenges, quantum computing as an applied science has come a long way, and the Chalmers team has played an instrumental role in pushing its barriers. Theyve added to the quantum computing toolbox and shown us new ways to use quantum mechanics. Now, were one step closer to accessible quantum computing.
As theory and experiments move faster, the future of quantum computing has never looked better. Quantum computers will deliver exponential speedups for a wide range of computational tasks in fields such as drug discovery, materials design, cryptography, and artificial intelligence. Coupled with advances in technologies like AI, these developments assure us that the world is on the brink of transformative changes that are hard to fully envision.
Click here for a list of the five best quantum computing companies.
Read more from the original source:
Quantum Computing One Step Closer to Reality by Leveraging Harmonic Oscillators - Securities.io
- Mathematician breaks down how to defend against quantum ... - Phys.Org [Last Updated On: February 28th, 2017] [Originally Added On: February 28th, 2017]
- Here Is Everything You Need to Know About Quantum Computers - Interesting Engineering [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- Quantum Computing Market Forecast 2017-2022 | Market ... [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- What is Quantum Computing? Webopedia Definition [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- Quantum computing is about to disrupt the government contracts market - Bloomberg Government (blog) [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- Scientists: We Have Detected the Existence of a Fundamentally New State of Matter - Futurism [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- What Sorts Of Problems Are Quantum Computers Good For? - Forbes [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- quantum computing - WIRED UK [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- Inside Microsoft's 'soup to nuts' quantum computing ramp-up - Computerworld Australia [Last Updated On: April 29th, 2017] [Originally Added On: April 29th, 2017]
- Molecular magnets closer to application in quantum computing - Next Big Future [Last Updated On: May 15th, 2017] [Originally Added On: May 15th, 2017]
- The Bizarre Quantum Test That Could Keep Your Data Secure - WIRED [Last Updated On: May 18th, 2017] [Originally Added On: May 18th, 2017]
- IBM boosts power of quantum computing processors as it lays ... - www.computing.co.uk [Last Updated On: May 22nd, 2017] [Originally Added On: May 22nd, 2017]
- IBM makes leap in quantum computing power - ITworld [Last Updated On: May 22nd, 2017] [Originally Added On: May 22nd, 2017]
- Toward mass-producible quantum computers | MIT News - MIT News [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Purdue, Microsoft Partner On Quantum Computing Research | WBAA - WBAA [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Tektronix AWG Pulls Test into Era of Quantum Computing - Electronic Design [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Google to Achieve "Supremacy" in Quantum Computing by the End of 2017 - Big Think [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Quantum Computing Becomes More Accessible - Scientific American [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Qudits: The Real Future of Quantum Computing? - IEEE Spectrum - IEEE Spectrum [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Alkermes and IBM's quantum computing. Who'll be the big winner? Malcolm Berko - Durham Herald Sun [Last Updated On: July 6th, 2017] [Originally Added On: July 6th, 2017]
- Quantum Computers Made Even More Powerful with New microchip generating 'Qudits' - TrendinTech [Last Updated On: July 8th, 2017] [Originally Added On: July 8th, 2017]
- Quantum Computing Record Broken - Wall Street Pit [Last Updated On: July 8th, 2017] [Originally Added On: July 8th, 2017]
- Technique for measuring and controlling electron state is a ... - UCLA Newsroom [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Quantum cheques could be a forgery-free way to move money - New Scientist [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Quantum-computer node uses two different ion species - physicsworld.com [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Quantum Computers vs Bitcoin How Worried Should We Be? - The Merkle [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Why you might trust a quantum computer with secretseven over ... - Phys.Org [Last Updated On: July 12th, 2017] [Originally Added On: July 12th, 2017]
- Physicists Take Big Step Towards Quantum Computing and ... - Universe Today [Last Updated On: August 1st, 2017] [Originally Added On: August 1st, 2017]
- Quantum Computing Market Worth 495.3 Million USD by 2023 | 08 ... - Markets Insider [Last Updated On: August 10th, 2017] [Originally Added On: August 10th, 2017]
- China uses a quantum satellite to transmit potentially unhackable data - CNBC [Last Updated On: August 10th, 2017] [Originally Added On: August 10th, 2017]
- Blind quantum computing for everyone - Phys.org - Phys.Org [Last Updated On: August 12th, 2017] [Originally Added On: August 12th, 2017]
- Quantum Computing Is Real, and D-Wave Just Open ... - WIRED [Last Updated On: August 12th, 2017] [Originally Added On: August 12th, 2017]
- Machine learning tackles quantum error correction - Phys.Org [Last Updated On: August 15th, 2017] [Originally Added On: August 15th, 2017]
- Quantum Internet Is 13 Years Away. Wait, What's Quantum Internet? - WIRED [Last Updated On: August 15th, 2017] [Originally Added On: August 15th, 2017]
- Physicists Have Made Exotic Quantum States From Light - Futurism [Last Updated On: August 16th, 2017] [Originally Added On: August 16th, 2017]
- $495.3 Million Quantum Computing Market 2017 by Revenue Source, Application, Industry, and Geography - Global ... - PR Newswire (press release) [Last Updated On: August 18th, 2017] [Originally Added On: August 18th, 2017]
- How quantum mechanics can change computing - The Conversation US [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- Introducing Australia's first quantum computing hardware company - Computerworld Australia [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- IEEE Approves Standards Project for Quantum Computing ... - insideHPC [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- Commonwealth Bank investing in Australia's first quantum computer company - Which-50 (blog) [Last Updated On: August 25th, 2017] [Originally Added On: August 25th, 2017]
- How quantum mechanics can change computing - San Francisco ... - San Francisco Chronicle [Last Updated On: August 25th, 2017] [Originally Added On: August 25th, 2017]
- Quantum Computing Is Coming at Us Fast, So Here's Everything You Need to Know - ScienceAlert [Last Updated On: August 27th, 2017] [Originally Added On: August 27th, 2017]
- Quantum computing event explores the implications for business - Cambridge Network [Last Updated On: August 30th, 2017] [Originally Added On: August 30th, 2017]
- Microsoft's Aussie quantum computing lab set to scale up next-gen ... - ARNnet [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- An Entirely New Type of Quantum Computing Has Just Been Invented - Futurism [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- Microsoft just upped its multi-million bet on quantum computing - ZDNet [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- Here's what quantum computing is and why it matters [Last Updated On: October 6th, 2017] [Originally Added On: October 6th, 2017]
- What will you actually use quantum computing for? | ZDNet [Last Updated On: October 11th, 2017] [Originally Added On: October 11th, 2017]
- Quantum Computing | Intel Newsroom [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Intel Takes First Steps To Universal Quantum Computing [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Qudits: The Real Future of Quantum Computing? - IEEE Spectrum [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- quantum computing - engadget.com [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Quantum computing - news.microsoft.com [Last Updated On: November 1st, 2017] [Originally Added On: November 1st, 2017]
- IBM's processor pushes quantum computing ... - engadget.com [Last Updated On: November 16th, 2017] [Originally Added On: November 16th, 2017]
- Yale Professors Race Google and IBM to the First Quantum ... [Last Updated On: November 16th, 2017] [Originally Added On: November 16th, 2017]
- Quantum Computing Is the Next Big Security Risk | WIRED [Last Updated On: December 8th, 2017] [Originally Added On: December 8th, 2017]
- Microsoft offers developers a preview of its quantum ... [Last Updated On: December 12th, 2017] [Originally Added On: December 12th, 2017]
- New silicon structure opens the gate to quantum computers [Last Updated On: December 14th, 2017] [Originally Added On: December 14th, 2017]
- Quantum Computing Explained | What is Quantum Computing? [Last Updated On: December 21st, 2017] [Originally Added On: December 21st, 2017]
- What is Quantum Computing? | SAP News Center [Last Updated On: December 23rd, 2017] [Originally Added On: December 23rd, 2017]
- Is Quantum Computing an Existential Threat to Blockchain ... [Last Updated On: December 25th, 2017] [Originally Added On: December 25th, 2017]
- IBM puts its quantum computer to work in relaxing, nerdy ASMR ... [Last Updated On: January 8th, 2018] [Originally Added On: January 8th, 2018]
- Quantum computing is going to change the world. Here's what ... [Last Updated On: January 8th, 2018] [Originally Added On: January 8th, 2018]
- The Era of Quantum Computing Is Here. Outlook: Cloudy ... [Last Updated On: January 26th, 2018] [Originally Added On: January 26th, 2018]
- What is quantum computing? - Definition from WhatIs.com [Last Updated On: February 5th, 2018] [Originally Added On: February 5th, 2018]
- Senate bills would make quantum computing a priority [Last Updated On: June 10th, 2018] [Originally Added On: June 10th, 2018]
- Two Quantum Computing Bills Are Coming To Congress [Last Updated On: July 5th, 2018] [Originally Added On: July 5th, 2018]
- Quantum Computing Market Research Report- Forecast 2022 | MRFR [Last Updated On: August 1st, 2018] [Originally Added On: August 1st, 2018]
- What Is Quantum Computing? The Complete WIRED Guide | WIRED [Last Updated On: August 22nd, 2018] [Originally Added On: August 22nd, 2018]
- Quantum Computing | USRA [Last Updated On: August 30th, 2018] [Originally Added On: August 30th, 2018]
- The quantum computing race the US cant afford to lose [Last Updated On: September 3rd, 2018] [Originally Added On: September 3rd, 2018]
- The reality of quantum computing could be just three years ... [Last Updated On: September 12th, 2018] [Originally Added On: September 12th, 2018]
- US takes first step toward a quantum computing workforce ... [Last Updated On: September 17th, 2018] [Originally Added On: September 17th, 2018]
- China bet big on quantum computing. Now the ... - money.cnn.com [Last Updated On: September 17th, 2018] [Originally Added On: September 17th, 2018]
- China bet big on quantum computing. Now the US races to ... [Last Updated On: October 26th, 2018] [Originally Added On: October 26th, 2018]
- A new type of quantum computer has smashed every record ... [Last Updated On: December 21st, 2018] [Originally Added On: December 21st, 2018]
- IBM unveils its first commercial quantum computer [Last Updated On: January 9th, 2019] [Originally Added On: January 9th, 2019]
- IBM thinks outside of the lab, puts quantum computer in a box [Last Updated On: January 11th, 2019] [Originally Added On: January 11th, 2019]
- Quantum Computing | The MIT Press [Last Updated On: January 11th, 2019] [Originally Added On: January 11th, 2019]
- CES 2019: IBM's Q System One Is the Rock Star Quantum ... [Last Updated On: January 13th, 2019] [Originally Added On: January 13th, 2019]