Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > A new phase in reading photons: A JQI photodetector beats the quantum limit by a factor of 4

The error rate is plotted as a function of the mean number of photons used to deliver the information. The standard quantum limit (SQL) is the red line. The light gray line is the SQL line if you take into account that individual photon detector stages used were ~72 percent efficient rather than 100 percent (with the detector efficiencies being 84 percent. In the business of detecting single photons, 84 percent is top of the line.) The error probabilities measured for the system (black points with error bars) fall well below the quantum limit, by about 6 decibels in the center of the curve. This is equivalent to saying that the JQI receiver is performing better than the SQL by a factor of about 4 in determining the phase of an incoming signal. That is, the JQI receiver achieves an error probability that is 4 times lower than the so-called "Standard Quantum Limit." This graph shows results for a system that implements 10 adaptive measurements. The two other lines on the chart show what the expected uncertainty would be for a perfect system (100 percent efficient detectors) and without any of the imperfections that would be encountered in any realistic implementation, and a hypothetical ultimate-limit on uncertainty derived by Helstrom.

Credit: NIST
The error rate is plotted as a function of the mean number of photons used to deliver the information. The standard quantum limit (SQL) is the red line. The light gray line is the SQL line if you take into account that individual photon detector stages used were ~72 percent efficient rather than 100 percent (with the detector efficiencies being 84 percent. In the business of detecting single photons, 84 percent is top of the line.) The error probabilities measured for the system (black points with error bars) fall well below the quantum limit, by about 6 decibels in the center of the curve. This is equivalent to saying that the JQI receiver is performing better than the SQL by a factor of about 4 in determining the phase of an incoming signal. That is, the JQI receiver achieves an error probability that is 4 times lower than the so-called "Standard Quantum Limit." This graph shows results for a system that implements 10 adaptive measurements. The two other lines on the chart show what the expected uncertainty would be for a perfect system (100 percent efficient detectors) and without any of the imperfections that would be encountered in any realistic implementation, and a hypothetical ultimate-limit on uncertainty derived by Helstrom.

Credit: NIST

Abstract:
"That's not what I meant": human communication is fraught with misinterpretation. Written out in longhand, words and letters can be misread. A telegraph clerk can mistake a dot for a dash. Noise will always be with us, but at least a new JQI (*) device has established a new standard for reading quantum information with a minimum of uncertainty.

A new phase in reading photons: A JQI photodetector beats the quantum limit by a factor of 4

College Park, MD | Posted on January 6th, 2013

Success has come by viewing light pulses not with a single passive detector with but an adaptive network of detectors with feedback. The work on JQI's new, more assured photonic protocol was led by Francisco Becerra and carried out in Alan Migdall's JQI lab. They report their results in Nature Photonics (**). Here are some things you need to know to appreciate this development.

HOW TO MODULATE?

Digital data, in its simplest form, can be read with a process called on-off keying: a detector senses the intensity of incoming bursts of electrons in wires or photons through fibers and assigns a value of 0 or 1. A more sophisticated approach to modulating a signal (not merely off/on) is to encode data in the phase of the pulse. In "phase-shift keying," information is encoded in the amount of phase shift imposed on a carrier wave; the phase of the wave is how far along the wave cycle you happen to be (say, at the top of a crest or the bottom of a trough in a sinusoidal, as in this figure).

WHAT KIND OF ALPHABET?

Larger words can be assembled from a small suite of symbols. The Roman alphabet has 26 letters, the Greek only 24. Binary logic, and most transistors, makes do with just a two-letter alphabet. Everything is a 0 or a 1, and larger numbers and letters and words are assembled from as many binary bits as are necessary. But what if we enlarged the alphabet from two to four? In quaternary logic more data can be conveyed in a single pulse. The cost of this increase is having to write and read 4 states of modulation (or 4 symbols). Even more efficient in terms of packing data, but correspondingly more difficult to implement, is logic based on 6 states, or 8, or any higher number. Digital data at its most basic---at the level of transistor---remains in binary form, but for communicating this data, higher number alphabets can be used. In fact, high-definition television delivery already involves high-level logic.

UNCERTAINTY

No matter what kind of logic is used, errors creep in. A detector doesn't just unequivocally measure a 0 or a 1. The reading process is imperfect. And even worse, the state of the light pulse is inherently uncertain, and that is a real problem when the light pulses belong to a set of overlapping states. This is illustrated in the figure below for binary and quaternary phase states.

On the left side of the figure, the measurement of the phase of a light pulse is depicted, where there are only two choices. Is the pulse in the alpha state or the -alpha state? Because the tails of one overlap the other there is a slight ambiguity that leads to uncertainty in which state a measurement indicates. On the right, four possible states are depicted on a complex-number graph (with real (Re) and imaginary (Im) axes). Here the overlap of the states is more complicated, but results in similar ambiguities of the measured states, seen mostly near the borders (decision threshold lines) between the states.

STANDARD QUANTUM LIMIT

Decades ago communications theory established a minimal uncertainty for the accurate transmission and detection of information encoded in overlapping states. The hypothetical minimal detection error using conventional schemes is called the standard quantum limit and it depends on things like how many photons of light comprise the signal, how many levels (binary, quaternary, etc.) need to be read out, and which physical property of light is used to encode the information, such as the phase.

But starting in the 1970s with physicist Carl W. Helstrom, some scientists have felt that the standard quantum limit could be circumvented. The JQI researchers do exactly this by using not a single passive photo-detector, but an active detection process involving a series of stages. At each stage, the current light signal strikes a partially-silvered mirror, which peels off a fraction of the pulse for analysis and the rest goes on to subsequent stages. At each stage the signal is combined with a separate reference oscillator wave used as a phase reference against which the signal phase is determined. This is done by shifting the reference wave by a known amount and letting it interfere with the signal wave at the beamsplitter. By altering that known shift, the interference pattern can reveal something about the phase of the input pulse.

ACTIVE DETECTION

By combining many such stages (see the figure below) and using information gained by previous stages to adjust the phase of the reference wave in successive stages, a better estimate of the signal phase can be obtained.

Detecting phase in this adaptive way, and implemented in a feedback manner, the JQI system is able to beat the standard quantum limit for a set of 4 states (quaternary) encoding information as a phase. These states are represented as fuzzy distributions arranged at different angles around a circle as seen in the figure above where the angles represent the phase of the light pulses.

The JQI noise-reduction achievement is depicted in the graph below. The error rate is plotted as a function of the mean number of photons used to deliver the information. The standard quantum limit (SQL) is the red line. The light gray line is the SQL line if you take into account that individual photon detector stages used were ~72% efficient rather than 100% (with the detector efficiencies being 84%. In the business of detecting single photons, 84% is top of the line.)

The error probabilities measured for the system (black points with error bars) fall well below the quantum limit, by about 6 decibels in the center of the curve. This is equivalent to saying that the JQI receiver is performing better than the SQL by a factor of about 4 in determining the phase of an incoming signal. That is, the JQI receiver achieves an error probability that is 4 times lower than the so-called "Standard Quantum Limit." This graph shows results for a system that implements 10 adaptive measurements. The two other lines on the chart show what the expected uncertainty would be for a perfect system (100% efficient detectors) and without any of the imperfections that would be encountered in any realistic implementation, and a hypothetical ultimate-limit on uncertainty derived by Helstrom.

To conclude, the JQI photon receiver features an error rate four times lower than perfect conventional receivers, over a wide range of photon number, and with discrimination for four states. The only previous detection below the quantum limit was for a very narrow range of photons and with only a 2-state protocol and only slightly below the SQL.

(**) "Experimental demonstration of a receiver beating the standard quantum limit for multiple nonorthogonal state discrimination," by F. E. Becerra, J. Fan, G. Baumgartner, J. Goldhar, J. T. Kosloski, and A. Migdall, Nature Photonics, published online 6 January 2013.

####

About Joint Quantum Institute
The Joint Quantum Institute (JQI) is operated jointly by the National Institute of Standards and Technology in Gaithersburg, MD and the University of Maryland in College Park.

For more information, please click here

Contacts:
Press contact at JQI:
Phillip F. Schewe

301-405-0989

Alan Migdall

301-975-2331

Copyright © Joint Quantum Institute

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

Gold shines through properties of nano biosensors: Researchers discover that fluorescence in ligand-protected gold nanoclusters is an intrinsic property of the gold particles themselves August 16th, 2017

Two Scientists Receive Grants to Develop New Materials: Chad Mirkin and Monica Olvera de la Cruz recognized by Sherman Fairchild Foundation August 16th, 2017

Scientists from the University of Manchester and Diamond Light Source work with Deben to develop and test a new compression stage to study irradiated graphite at elevated temperatures August 15th, 2017

Physics

Sensing technology takes a quantum leap with RIT photonics research: Office of Naval Research funds levitated optomechanics project August 10th, 2017

'Perfect Liquid' Quark-Gluon Plasma is the Most Vortical Fluid: Swirling soup of matter's fundamental building blocks spins ten billion trillion times faster than the most powerful tornado, setting new record for "vorticity" August 4th, 2017

The first light atomic nucleus with a second face July 20th, 2017

X-ray photoelectron spectroscopy under real ambient pressure conditions June 28th, 2017

Govt.-Legislation/Regulation/Funding/Policy

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

2-faced 2-D material is a first at Rice: Rice University materials scientists create flat sandwich of sulfur, molybdenum and selenium August 14th, 2017

Engineers pioneer platinum shell formation process – and achieve first-ever observation August 11th, 2017

Moving at the Speed of Light: University of Arizona selected for high-impact, industrial demonstration of new integrated photonic cryogenic datalink for focal plane arrays: Program is major milestone for AIM Photonics August 10th, 2017

Discoveries

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

Gold shines through properties of nano biosensors: Researchers discover that fluorescence in ligand-protected gold nanoclusters is an intrinsic property of the gold particles themselves August 16th, 2017

Fewer defects from a 2-D approach August 15th, 2017

Scientists from the University of Manchester and Diamond Light Source work with Deben to develop and test a new compression stage to study irradiated graphite at elevated temperatures August 15th, 2017

Announcements

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

Gold shines through properties of nano biosensors: Researchers discover that fluorescence in ligand-protected gold nanoclusters is an intrinsic property of the gold particles themselves August 16th, 2017

Two Scientists Receive Grants to Develop New Materials: Chad Mirkin and Monica Olvera de la Cruz recognized by Sherman Fairchild Foundation August 16th, 2017

Scientists from the University of Manchester and Diamond Light Source work with Deben to develop and test a new compression stage to study irradiated graphite at elevated temperatures August 15th, 2017

Tools

Scientists from the University of Manchester and Diamond Light Source work with Deben to develop and test a new compression stage to study irradiated graphite at elevated temperatures August 15th, 2017

FRITSCH • Milling and Sizing! Innovations at POWTECH 2017 - Hall 2 • Stand 227 August 9th, 2017

New Quattro Field Emission ESEM Emphasizes Versatility and Ease of Use: Thermo Scientific Quattro ESEM allows materials science researchers to study nanoscale structure in almost any material under a range of environmental conditions August 8th, 2017

Thermo Fisher Scientific’s New Talos F200i S/TEM Delivers Flexible, High-Performance Imaging: New compact S/TEM can be configured to meet specific imaging and analytical requirements for materials characterization in research laboratories August 8th, 2017

Photonics/Optics/Lasers

Moving at the Speed of Light: University of Arizona selected for high-impact, industrial demonstration of new integrated photonic cryogenic datalink for focal plane arrays: Program is major milestone for AIM Photonics August 10th, 2017

Sensing technology takes a quantum leap with RIT photonics research: Office of Naval Research funds levitated optomechanics project August 10th, 2017

High resolution without particle accelerator: A first for physics -- University of Jena physicists are first to achieve optical coherence tomography with XUV radiation at laboratory scale August 7th, 2017

Simultaneous Design and Nanomanufacturing Speeds Up Fabrication: Method enhances broadband light absorption in solar cells August 5th, 2017

Research partnerships

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

2-faced 2-D material is a first at Rice: Rice University materials scientists create flat sandwich of sulfur, molybdenum and selenium August 14th, 2017

Moving at the Speed of Light: University of Arizona selected for high-impact, industrial demonstration of new integrated photonic cryogenic datalink for focal plane arrays: Program is major milestone for AIM Photonics August 10th, 2017

Sensing technology takes a quantum leap with RIT photonics research: Office of Naval Research funds levitated optomechanics project August 10th, 2017

Quantum nanoscience

Sensing technology takes a quantum leap with RIT photonics research: Office of Naval Research funds levitated optomechanics project August 10th, 2017

Nanocrystalline LEDs: Red, green, yellow, blue ... August 7th, 2017

Scientists discover new magnet with nearly massless charge carriers July 29th, 2017

Ultracold molecules hold promise for quantum computing: New approach yields long-lasting configurations that could provide long-sought “qubit” material July 27th, 2017

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project